Sofc-conduction

ABSTRACT

A solid oxide fuel cell (SOFC) system includes high thermal conductivity materials such as copper to increase thermal energy transfer by thermal conduction. The copper is protected from oxidation by nickel electroplating and protected from thermal damage by providing oxidation resistant liners inside combustion chambers.

1 COPYRIGHT NOTICE

A portion of the disclosure of this patent document may contain materialthat is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent files or records, but otherwise reserves all copyrightrights whatsoever. The following notice shall apply to this document: ©2020 Upstate Power Inc.

2 BACKGROUND OF THE TECHNOLOGY 2.1 Field of the Technology

The exemplary, illustrative, technology herein relates to Solid OxideFuel Cell (SOFC) systems, methods of use, and methods of manufacturingSOFC systems. In particular, the exemplary, illustrative technologyrelates to improved systems and methods for thermal energy managementwithin the SOFC system.

2.2 The Related Art

A conventional SOFC system includes a hot zone, which contains or atleast partially encloses system components that are maintained at higheroperating temperatures, e.g. above 350 or 500° C., during operation,depending on the SOFC technology. The hot zone houses a SOFC energygenerator or solid oxide fuel cell stack. Conventional SOFC fuel cellstacks are formed by one or more fuel cells with each cell participatingin an electro-chemical reaction that generates an electrical current.The fuel cells are electrically interconnected in series or in parallelas needed to provide a desired output voltage of the cell stack. Eachfuel cell includes three primary layers, an anode layer or fuelelectrode, a cathode layer or air electrode and an electrolyte layerthat separates the anode layer from the cathode layer.

The anode layer is exposed to a gaseous or vaporous fuel that at leastcontains hydrogen gas (H₂) and/or carbon monoxide (CO). At the same timethe cathode layer is exposed to a cathode gas such as air or any othergas or vaporous oxygen (O₂) source. In the cathode layer oxygen (air)supplied to the cathode layer receives electrons to become oxygen ions(O⁻²). The oxygen ions pass from the cathode layer to the anode layerthrough the ceramic electrolyte layer. At the triple phase boundary, inthe anode layer, hydrogen (H₂) and/or carbon monoxide (CO) supplied tothe anode layer by the fuel react with oxide ions to produce water andcarbon dioxide and electrons emitted during this reaction produceelectricity and heat. Other reaction by products in the fuel stream mayinclude methane, ethane or ethylene. The electricity produced by theelectro-chemical reaction is extracted to DC power terminals to power anelectrical load.

Common anode materials include cermets such as nickel and doped zirconia(Ni-YSZ), nickel and doped ceria (Ni-SDC and or Ni-GDC), copper anddoped ceria. Perovskite anode materials such asLa_(0.75)Sr_(0.25)Cr_(0.5)Mn_(0.5)O_(3-δ) (LSCM) and other ABO₃structures are also usable. Common cathode materials include LanthanumStrontium Cobalt Oxide (LSC), Lanthanum Strontium Cobalt Iron Oxide(LSCF) and Lanthanum Strontium Manganite (LSM). The electrolyte layer isan ion conducting ceramic, usually an oxygen ion conductor such asyttria doped zirconia or gadolinium doped ceria. Alterably theelectrolyte layer is a proton conducting ceramic such as barium ceratesor barium ziconates. The electrolyte layer acts as a near hermeticbarrier to prevent the fuel and air from mixing and combusting.

Conventional SOFC systems use cross flow or parallel flow heatexchangers, commonly referred to as recuperators, to heat cathode gasses(air) entering the SOFC system. The gas flow heat exchangers heat coolair entering the hot zone by exchanging thermal energy between the coolentering air and hot exhaust gas exiting the hot zone. Air to air crossflow heat exchangers are inefficient as compared with thermal energytransfer by thermal conduction. Conventional SOFC power generatingsystems largely rely on incoming cathode air flow to manage thermalenergy distribution. However, the cathode air flow rate isconventionally selected to redistribute thermal energy instead ofoptimizing a SOFC reaction. When selecting the cathode air volume rate(e.g., liters per second) or mass flow rate (e.g., kg/s) to optimize theSOFC reaction, the required volume or mass flow rates is significantlyless than is required to redistribute thermal energy and in some casesthermal energy distribution requires 300% greater cathode air flow ratesthan would be required to for SOFC reaction. One consequence of usinghigher volume air flow rates in the SOFC system is a drop in powergeneration efficiency due to the energy required to move the excess airflow. In addition, the thermal energy used to heat the excessive airflow is not available to heat the SOFC stack and other surfaces,especially during start up.

In conventional SOFC systems, a recuperator or gas counter flow heatexchanger, is disposed to receive hot gases exiting from a tail gascombustion chamber and to receive cool gases entering into the SOFCsystem in counter flow conduits separated by a common wall. Again,convection and radiation are the dominant thermal energy transfermechanisms as hot gases from the combustor heat conduit walls as theypass to an exit port and the conduit walls heat incoming air. In short,the thermal energy exchange both inside the tail gas combustor andinside the recuperator is not efficient. The result is that conventionalSOFC systems are notoriously difficult to control and often develop hotspots, e.g. in the combustion enclosures, that can damage the enclosurewalls even burning through walls when a combustion enclosure wall getstoo hot. Alternately when the temperature of the SOFC system is lowered,e.g. by reducing a fuel input flow rate, and increasing an input cathodeair flow rate to cool hot spots, the SOFC reaction is altered whichoften leads to undesirable operation such as reduced electrical poweroutput, incomplete fuel processing which results in carbon formation onanode surfaces which ultimately leads to decreased electrical output andeventual failure.

To better address hot and cold spots conventional SOFC systems ofteninclude a plurality of thermocouples or thermistors disposed at varioussystem points to monitor temperature and adjust operation in order toavoid hot spots and prevent cold spots. However, the temperature sensingand monitoring systems are costly and prone to failure due to the highoperating temperatures of the SOFC systems (e.g. 350-1200° C. near thetail gas combustion chamber). Moreover, the need to modulate fuel inputas a measure to avoid damaging the SOFC system leads to inefficient andvariable electrical power output. Thus, there is a need in the art toavoid thermal gradients and eliminate hot spots in order to avoiddamaging the SOFC system and in order to deliver more consistentelectrical power output with improve power generation efficiency.Additionally, there is a need to provide a more efficient and passivemethod for thermal energy management in SOFC system that does not relymodifying fuel and air flow rates to manage thermal energy distribution,e.g. to reduce the temperature of hot spots.

Conventional SOFC systems use heat and corrosion resistant materials tosurvive the effects of extended operation at high temperatures and theseverely corrosive environment which continuously oxidizes metalsurfaces sometimes to the point of failure. Use of specialty hightemperature corrosion resistant nickel-chromium alloys such as Inconel,Monel, Hastelloy or the like are commonly used in SOFC systems. However,while these materials perform well in the high temperature corrosionprone environment of SOFC power generator these material tend to have avery low coefficient of thermal conductivity, e.g. as compared to highlythermally conduct materials such as copper, aluminum, molybdenum orallows thereof. As an example, Inconel has a thermal conductivityranging from 17-35 W/(m° K) over a temperature range of 150 to 875° C.as compared to copper which has a thermal conductivity approximatelyranging from 370 W/(m° K) at 500° C. and 332 W/m° K at 1027° C. Thus,copper has a thermal conductivity that is more than 10 times the thermalconductivity of Inconel. While copper provides increased thermalconductivity over high temperature non-corrosive metal alloys, copper ishighly susceptible to breakdown by oxidation at high temperatures andhas thus far been avoided as a SOFC enclosure material.

3 BRIEF SUMMARY OF THE TECHNOLOGY

The present technology overcomes the problems associated withconventional SOFC systems by providing various embodiments of animproved SOFC system that includes configurations of a hot zoneenclosure assembly (8042) formed with a U-shaped primary enclosure wallassembly (8045) and a hot zone enclosure assembly (12042) that includestwo L-shaped primary enclosure wall assemblies (12045) as well as otherhot zone enclosure assembly embodiments (14042, 15042) that utilizes oneor more U-shaped and L-shaped primary enclosure wall assemblies. Eachprimary enclosure wall assembly is formed to enclose a SOFC stack(8005), a cathode chamber (8055, 12055) and a combustion region (8030)located above the fuel output end (8025) of each individual fuel cell.Each primary enclosure wall assembly includes a combustion region wall(8060, 12060) that is formed to bound the combustion region and at leastone opposing primary enclosure sidewalls (8065, 8070, 12070) that eachextends from an edge of the combustion region wall (8060, 12060) to thecathode input end of the individual fuel cells such that the SOFC stackis enclosed by the primary enclosure wall assembly along the input end(8020) at least along the full longitudinal length (x) of the SOFCstack.

Each primary enclosure wall (8060, 12060), (8065) and (8070, 12070)includes a thermally conductive core (8200) protected from oxidation byouter layers applied to exposed surfaces thereof. The thermallyconductive core (8200) comprises one or more materials having acoefficient of thermal conductivity that is greater than 100 W/(m° K)and preferably greater than 200 W/(m° K). The thermally conductive coreis formed from copper or molybdenum, or aluminum copper or a coppernickel alloy or a combination thereof. The thermally conductive core hasa thickness in the range of 0.127 to 6.0 mm, (0.005 to 0.24 inches).

To prevent oxidation of the thermally conductive core (8200), each ofthe core portions (8205, 8210, 8215, 12010, 12015, 12017) is protectedby a protective layer applied over or attached to exposed surfaces ofthe thermally conductive core. The protective layer may include nickelplating applied to surfaces of each core portion by an electro-platingprocess to a thickness of at least 0.0005 inches and ranging up to 0.002inches. Alternately, or additionally, the protective layer comprises oneor more metal sheets disposed in mating contact with exposed surfaces ofeach of the three core portions (8205), (8210, 12010) and (8215, 12015,12017). The metal sheets are applied directly to uncoated surfaces ofthe thermally conductive core or are applied over electroplated surfacesof the thermally conductive core. An inner protective sheet metal layer(8220) is fabricated as a U-shaped structure formed to attach to theinside surfaces of each of the three core portions (8205), (8210),(8215) with the inside surfaces of the inner protective layer (8220)face the SOFC stack. An outer protective layer (8250) comprises twosubstantially identical outer side wall portions (8255) and (8260) andan outer top portion (8265). The three outer protective layer portions,when joined together with each other, and joined together withcorresponding outer surfaces of the thermally conductive core form aU-shaped sheet metal structure shaped to attach to and protect theoutside surfaces of the thermally conductive core (8200) from exposureto oxygen rich cathode air flow. Preferably, the inside surfaces of theouter protective layer are in mating contact with corresponding outsidesurfaces of the thermally conductive core that face away from the SOFCstack. A second embodiment of the inner protective layer (12220) and anouter protective layer (12250) is also described herein.

Each wall portion of the inner protective layer and of the outerprotective layer is fabricated from ferritic steel such as Alloy 18 SR®Stainless Steel, e.g. distributed by Rolled Metal Products, of Alsip,Ill., US. The Alloy 18 SR® Stainless Steel is an aluminum stabilizedferritic stainless steel designed for high temperature applications withimproved scaling and corrosion resistance which is achieved by theaddition of aluminum in a range of 1.5 to 2.5 weight percent. The Alloy18 SR® Stainless Steel is preferred because under operating temperaturesand conditions of the SOFC system (8000) the added aluminum contentadvantageously forms a surface layer of aluminum oxide which preventsoxidation of exposed surfaces of the inner protective layer and of theouter protective layer, which prevents oxidation and prevents chromiumfrom leaching from the Alloy 18 SR® Stainless Steel.

Each hot zone enclosure assembly (8042, 12042, 14042, 15042) optionallyinclude end walls (8080, 8085) and a bottom wall (8075) that furtherenclose the cathode chamber (8055, 12055) or the cathode chamber isfurther enclosed by an intermediate enclosure (9000) which includes endwalls (9020, 9025) and a bottom wall (9010). The end walls (8080, 8085)and a base wall (8075) may include a thermally conductive coreconfigured with protective layers provided prevent oxidation damage tothe core material.

4 BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present technology will best be understood from adetailed description of the technology and example embodiments thereofselected for the purposes of illustration and shown in the accompanyingdrawings in which:

FIG. 1 depicts a schematic view of a first exemplary SOFC systemaccording to the present technology.

FIG. 2 depicts a schematic view of an exemplary hot zone of a SOFCsystem according to the present technology.

FIG. 3 depicts a schematic view of exemplary fuel flow pathways of aSOFC system according to the present technology.

FIG. 4 depicts a schematic view of exemplary air flow pathways of a SOFCsystem according to the present technology.

FIG. 5A depicts a section view taken through a first exemplary hot zoneexternal wall of a SOFC system according to the present technology.

FIG. 5B depicts a section view taken through a second exemplary hot zoneexternal wall of a SOFC system according to the present technology.

FIG. 5C depicts a section view taken through an exemplary bottom tubesupport wall including a thermally conductive mass of a SOFC systemaccording to the present technology.

FIG. 5D depicts a section view taken through an exemplary combustionregion end wall including a thermally conductive mass of a SOFC systemaccording to the present technology.

FIG. 5E depicts a section view taken through an exemplary combustionregion bottom wall including a thermally conductive mass of a SOFCsystem according to the present technology.

FIG. 6 depicts a schematic top section view of a SOFC system having aplurality of rod shaped fuel cells arranged in two concentric circularpatterns according to the present technology.

FIG. 7A schematically depicts a first improved fuel cell system thatincludes a first U-shaped primary enclosure wall assembly disposed overa single SOFC stack according to the present technology.

FIG. 7B schematically depicts the first improved fuel system of FIG. 7Awith dashed lines with arrow heads showing syngas flow and thermallyconductive heat flow through the U-shaped primary enclosure and withsolid lines with arrow heads showing cathode gas flow and radiateemission from high temperature regions, according to the presenttechnology.

FIG. 8A depicts an isometric transparent view of an intermediateenclosure for a hot zone assembly according to the present technology.

FIG. 8B depicts a section view taken through the primary enclosure wallassembly according to the present technology.

FIG. 9A depicts an isometric side view of an improved hot zoneconfiguration according to the present technology.

FIG. 9B depicts a detailed isometric side view of cathode flow passagesfor receiving a cathode into the hot zone enclosure assembly accordingto the present technology.

FIG. 9C depicts an exploded isometric view of the primary enclosureassembly according to the present technology.

FIG. 10A schematically depicts a SOFC stack test fixture used to measurefuel cell temperature at five points along the SOFC stack axis whenoperating the text fixture fuel cell to generate DC current output.

FIG. 10B graphically depicts a comparison of fuel cell temperature atthe five points along the SOFC stack axis when operating the testfixture without a thermally conductive core, shown in black, and whenoperating the test fixture with a thermally conductive core layerinstalled, shown cross-hashed.

FIG. 11A graphically depicts temperature measurements at five locationsalong a SOFC stack axis over a 2.5-hour startup and shut down cyclewithout the thermally conductive core of the present technology.

FIG. 11B graphically depicts temperature measurements at five locationsalong a SOFC stack axis over a 2.5-hour startup and shut down cycle withthe thermally conductive core of the present technology.

FIG. 12 schematically depicts a fuel cell system that includes aT-shaped primary enclosure wall assembly disposed over two SOFC stacksaccording to an aspect of the present technology.

FIG. 13 depicts an isometric side view of a hot zone enclosure assemblyincluding two halves of the T-shaped primary enclosure wall with eachhalf enclosing a SOFC stack and other cathode chamber portions accordingto an aspect of the present technology.

FIG. 13A depicts an isometric side view of an assembled L-shaped primaryenclosure wall assembly according to an aspect of the presenttechnology.

FIG. 13B depicts an exploded isometric side view of a half of theT-shaped primary enclosure wall assembly according to an aspect of thepresent technology.

FIG. 14 schematically depicts a fuel cell system that includes aL-shaped primary enclosure wall assembly disposed over one SOFC stackaccording to an aspect of the present technology.

FIG. 15 schematically depicts a fuel cell system that includes two SOFCstacks each enclosed by a U-shaped primary enclosure wall assemblyaccording to an aspect of the present technology.

FIG. 16A depicts a side isometric view of an outer enclosure forenclosing a hot zone assembly of FIGS. 12, 14, and 15 according to anaspect of the present technology.

FIG. 16B depicts an exploded side isometric view of an outer enclosureand an intermediate enclosure for enclosing a hot zone assembly of FIGS.12, 14, and 15 according to an aspect of the present technology.

FIG. 17 depicts an exploded side isometric view of an intermediateenclosure for enclosing a hot zone assembly of FIGS. 12, 14, and 15according to an aspect of the present technology.

4.1 DEFINITIONS

The following definitions are used throughout, unless specificallyindicated otherwise:

TERM DEFINITION Hastelloy A group of alloys comprising predominantlymetal nickel plus molybdenum, chromium, cobalt, iron, copper, manganesetitanium, zirconium, aluminum and tungsten in varying percentagesincluding zero in some alloys. Hastelloy alloys are primarily used foreffective survival under high temperature and or high stress in moderateto severely corrosive environments. Available from Haynes InternationalInc. of Kokomo IN, USA. Monel A group of alloys comprising up to 67%metal nickel and about 30% copper with smaller amounts of iron,manganese, carbon and silicon. Monel is used for its resistance tocorrosion. Available from Special Metals Corp. of New Hartford NY, USA.SOFC Solid Oxide Fuel Cell Inconel A family of austeniticnickel-chromium alloys comprising nickel 40-70% chromium 14-30%, iron3-9% manganese 0.3-1% plus silicon, carbon, sulfur and other elementsused for its resistance to oxidation and corrosion and strength over awide range of temperatures. When heated, Inconel forms a thick stablepassivating oxide layer protecting the surface from further attack.Attractive for high temperature applications to reduce creep. Availablefrom Special Metals Corp. of New Hartford NY, USA. Cermet Any of a classof heat-resistant materials made of ceramic and sintered metal. Oftenformed and sintered as a ceramic oxide mixture and converted through thereduction from an oxide ceramic to the metallic phase. (NiO—YSZ →Ni—YSZ) Perovskite A ternary material with the general structureA^([12])B^([6])X-3^([6]) same type of crystal structure as calciumtitanium oxide (CaTi0₃).

4.2 ITEM NUMBER LIST

The following item numbers are used throughout, unless specificallyindicated otherwise.

ITEM NUMBER DESCRIPTION 100 SOFC system 105 Hot zone 110 Cold zone 115Enclosure walls 120 Hot zone cavity 125 Air gap 130 Thermal insulationlayer 135 Fuel cell stack 140 DC current output terminals 145Electrolyte layer 150 Anode layer 155 Cathode layer 157 Thermocoupletemperature sensor 160 Supply fuel input line 165 Fuel reformer 170 Airinput line 175 Recuperator 180 Combustor 185 Exhaust port 190 Electroniccontroller 195 Cold start module 197 Supply fuel delivery controller 198Air delivery controller 2000 Hot zone 2002 Hot zone enclosure side wall2004 Disc-shaped top wall 2005 SOFC stack 2006 Disc-shaped bottom wall2010 Hot zone cavity 2012 Thermal insulation layer 2015 Hot zoneenclosure walls 2020 Reformer 2025 Supply fuel and air mixture 2027 Fuel(e.g., reformate) 2030 Reformer enclosure walls 2035 Catalyzing cavity2040 Catalyzing medium 2045 Reformer input port 2050 Reformer exit port2055 Fuel input manifold 2060 Longitudinal axis 2065 Annular thermalinsulating element 2070 Top tube support wall 2075 Bottom tube supportwall 2080 Fuel cells 2085 Annular tube wall 2090 Cathode chamber 2095Top end cap 2100 Bottom end cap 2105 Attaching end 2110 Journal-shapedsupporting end 2115 Cell input port 2120 Cell output port 2125Electrical lead 2130 Electrical lead 2135 Tail gas combustion region orchamber 2140 Combustor region end wall 2145 Cathode feed tube 2150Combustor exit port 2155 Air gap 2160 Thermally conductive mass 2165 Hotzone exit port 2170 Fuel input manifold top wall 2175 Thermallyconductive mass 2180 Thermally conductive mass 2185 Combustor baffle2200 Incoming air 2205 Air input port 2210 Recuperator chamber 2215Recuperator baffle 2225 Air input port 2230 Recuperator air input port2235 Recuperator air output port 2240 Cathode chamber air input port2245 Cathode chamber air output port 2300 Cold start combustor 2305Annular cold start combustion chamber 2310 Combustor inlet port 2315Startup fuel 2320 Igniter 2325 Startup combustor exit port 5005 Sectionof wall 2002 5010 Copper core 5015 Nickel layer 5020 Nickel layer 5025Sidewall recuperator chamber 5030 Hastelloy liner element 5040 Sectionof bottom tube wall 5045 Monel liner element 5050 Hastelloy linerelement 5055 Section of wall 2140 5060 Hastelloy liner element 5065Monel liner element 5070 Section of fuel input manifold top wall 5075Nickel layer 5080 Hastelloy layer 7000 SOFC system 7010 Cathode chamber7015 Hot zone enclosure wall 7020 Insulation layer 7025 Cathode feedtube 7030 Center axes 7035 Inner circular pattern 7040 Inner rod shapedfuel cells 7045 Outer circular pattern 7050 Outer rod shaped fuel cells16000 Outer enclosure 16002 Bottom outer enclosure wall 8000 SOFC hotzone 8005 SOFC stack 8010 Fuel Cell 8015 Fuel input manifold 8020 Fuelinput end 8025 Fuel output end 8030 Combustion region 8035 Fuel reformer8040 Fuel delivery conduit 8042 Hot zone enclosure assembly 8045U-shaped primary enclosure wall assembly 8050 Supply fuel 8055 Cathodechamber 8060 Combustion region wall 8065 Primary enclosure sidewall 8070Primary enclosure sidewall 8075 Hot zone enclosure base wall 8080 Hotzone enclosure end wall 8085 Hot zone enclosure end wall 8095 Cathodeflow passage 8100 System coordinate axes diagram 8140 Middle volumecathode chamber 8142 Lower volume cathode chamber 8145 Startup fuelinput conduit 8150 Fuel 8152 Startup fuel 8155 Burner element 8160 Fuelignitor element 8200 Thermally conductive core 8205 Core side wallportion 8210 Core side wall portion 8215 Core top wall portion 8220Inner protective layer 8225 Inner top wall portion 8230 Inner side wallportion 8235 Inner side wall portion 8240 Inner side wall bottom edge8245 Inner side wall bottom edge 8250 Outer protective layer 8255 Outerside wall portion 8260 Outer side wall portion 8265 Outer top wallportion 8270 Outer side wall bottom edge 8275 Outer side wall bottomedge 8280 Inner protective layer 8285 Outer protective layer 9000Intermediate enclosure 9005 Intermediate enclosure top wall 9010Intermediate enclosure bottom wall 9015 Intermediate enclosure side wall9020 Intermediate enclosure side wall 9022 Cathode input manifold sidewall 9024 Cathode chamber side wall 9025 Intermediate enclosure end wall9030 Intermediate enclosure end wall 9035 Fuel access port 9040 Cathodeinput port 9045 Hot zone exhaust port 9050 Recuperator Chamber 9055 Hotzone exhaust conduit 9059 Bottom wall of exhaust conduit 9060 Combustionexhaust port 9065 Recuperator exit port 9070 Cathode input manifold 9075Shared wall 9080 Baffle 10000 Test fixture 10005 Fuel cell 10010 Fuelinput manifold 10030 Star symbols 10035 Black Bars 10040 White Bars10045 Legend 10050 Dashed lines (indicating related thermocouple) 10055Legend 12000 SOFC hot zone 12042 Hot zone enclosure assembly 12045L-shaped primary enclosure wall assembly 12055 Cathode chamber 12060Combustion region wall 12062 Combustion region curved wall portion 12064Combustion region flat top wall portion 12070 Primary enclosure sidewall12200 Thermally conductive core 12210 Core side wall portion 12215 Corecurved wall portion 12217 Core top wall portion 12220 Inner protectivelayer 12225 Inner protective layer portion 12227 Inner protective layerportion 12230 Inner protective layer portion 12250 Outer protectivelayer 12260 Outer protective layer portion 12265 Outer protective layerportion 12267 Outer protective layer portion 13070 Cathode inputmanifold 14000 SOFC hot zone 14042 L-shaped hot zone enclosure assembly14070 Cathode input manifold 15000 SOFC hot zone 15042 Double U-shapedhot zone enclosure assembly 15070 Cathode input manifold 16005 Top outerenclosure wall 16010 Side outer enclosure wall 16015 Side outerenclosure wall

4.3 DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring to FIG. 1, a schematic diagram of a first embodiment of thepresent technology depicts a Solid Oxide Fuel Cell (SOFC) system (100).The system (100) includes a hot zone (105), that includes at least oneSOFC fuel cell and preferably a plurality of fuel cells forming a SOFCstack maintained at a high operating temperature, and a cold zone (110)that includes fuel input and exhaust modules, a DC power output moduleand other control elements. Hot zone enclosure walls (115) are disposedto enclose a hot zone cavity (120) therein. A thermal insulation layer(130) surrounds the enclosure walls (115) to thermally insulate the hotzone (105). An air gap (125) is provided between the thermal insulationlayer (130) and a side wall of the hot zone enclosure walls (115) andthe air gap provides a gas flow conduit for gases to flow over outersurfaces of the hot zone enclosure walls.

According to an important aspect of the present technology, the hot zoneenclosure walls (115) and associated thermal energy management elementsdescribed below are in thermal communication with each other in order toprovide thermally conductive pathways for thermal energy transfer to allregions of the hot zone by thermal conduction through the hot zoneenclosure walls (115). More specifically the hot zone enclosure walls(115) and any thermal energy management elements, described below,comprise materials having a high coefficient of thermal conductivity,e.g. between 100 and 300 W/(m° K), and preferably above 200 W/(m° K) attemperatures ranging from 350 to 1200° C. Accordingly, the hot zoneenclosure external walls and other thermal energy management elements,described below, are fabricated from one or more of copper, molybdenum,aluminum copper, copper nickel alloys or a combination thereof.Specifically, the hot zone enclosure walls (115) and associated thermalenergy management elements are configured to provide thermally conducivepathways for rapid conduction of thermal energy from one area of the hotzone to another. More specifically the hot zone enclosure walls (115)and associated thermal energy management elements are configured tomanage thermal energy within the hot zone by rapidly conducting thermalenergy from high temperature areas of the hot zone to lower temperatureareas of the hot zone in order to ensure that the entire hot zone ismaintained at a more uniform temperature than would be typical oftraditional SOFC systems.

An electrochemical energy generator or fuel cell stack (135) comprisingone or more Solid Oxide Fuel Cells (SOFCs) or other types of fuel cellsis enclosed within the hot zone (105) and supported with respect to theenclosure walls (115) by one or more support elements, described below.The fuel cell stack (135) includes one or more fuel cells with each cellparticipating in an electro-chemical reaction that generates anelectrical current. The fuel cells are electrically interconnected inseries or in parallel as needed to provide a desired output voltage ofthe cell stack (135). Each fuel cell includes three primary layers, ananode layer or fuel electrode (150), a cathode layer or air electrode(155) and an electrolyte layer (145) that separates the anode layer fromthe cathode layer.

The anode layer (150) is exposed to a reactant such as a gaseous orvaporous reformate that at least contains hydrogen gas (H₂) and/orcarbon monoxide (CO). At the same time the cathode layer (155) isexposed to air or vaporous oxygen (O₂) source or any other oxidizinggas. In the cathode layer (155) oxygen (air) supplied to the cathodelayer receives electrons to become oxygen ions (O⁻²). The cathodereaction is 1/2O₂+2e⁻=O⁻², sometimes written as O^(II).

The oxygen ions pass from the cathode layer to the anode layer (150)through the electrolyte layer (145). In the anode layer hydrogen (H₂)and/or carbon monoxide (CO) supplied to the anode layer by the fuelreact with oxide ions to produce water and carbon dioxide and electronsemitted during this reaction produce electricity and heat. Theelectricity produced by the electro-chemical reaction is extracted to DCcurrent output terminals (140) to power an electrical load.

Common anode materials include cermets such as nickel and dopedzirconia, nickel and doped ceria, copper and ceria. Perovskite anodematerials such as Sr₂Mg_(1-x)MnxMoO_(6-δ) orLa_(0.75)Sr_(0.25)Cr_(0.5)Mn_(0.5)O_(3-δ) are also usable. Commoncathode materials include Lanthanum Strontium Cobalt Oxide (LSC),Lanthanum Strontium Cobalt Iron Oxide (LSCF) and Lanthanum StrontiumManganite (LSM). The electrolyte layer is an ion conducting ceramic,usually an oxygen ion conductor such as yttria doped zirconia orgadolinium doped ceria. Alterably the electrolyte layer is a protonconducting ceramic such as barium cerates or barium ziconates. Theelectrolyte layer acts as a near hermetic barrier to prevent the fueland air from mixing and combusting.

Generally each fuel cell is configured with one of the anode layer(150), the cathode layer (155) or the electrolyte layer (145) formed asa support or mechanically structural element and the other two layersare coated onto the support element e.g. by dipping, spraying or thelike. Various support element structures are usable including onenon-limiting example embodiment shown in FIG. 2 wherein each fuel cellcomprises an anode support element configured as a hollow tube forming acylindrical gas conduit wherein the anode layer (150) forms the insidediameter of the cylindrical conduit, the ceramic electrolyte layer (145)is coated over the outside diameter of the structural anode layer (150)and the cathode layer (155) is coated over the outside diameter of theelectrolyte layer (145).

A fuel at least comprising hydrogen (H₂) and/or carbon monoxide (CO)flows through the hollow ceramic tube in contact with the anode layerand air flows over and outside surface of the hollow tube in contactwith the cathode layer. Electrical current is generated as describedabove.

While the specific cell stack of FIG. 2 comprises a plurality of tubularfuel cells, other cell stacks formed by fuel cells having differentknown form factors are usable without deviating from the presenttechnology. These may include a fuel cell stack (135) formed from aplurality of flat sheet type fuel cells formed in a stack with eachcells including a sheet shaped support layer with the other layerscoated onto the support layer and a separator disposed between adjacentflat support layer with other layers coated onto the support layer.

A supply fuel input line (160) delivers a supply fuel (8050) comprisinga gaseous or vaporous hydrocarbon fuel received from a supply fuelcontainer stored in the cold zone (110) or from an external supply fuelsource. A supply fuel delivery controller (197) in communication with anelectronic controller (190) is disposed along the supply fuel input line(160) in the cold zone to regulate supply fuel input volume or mass flowrate as needed to control the supply fuel input rate and to mix thesupply fuel with air. The supply fuel input line (160) delivers thesupply fuel air mixture (2025) into a fuel reformer (165) for fuelprocessing. The supply fuel and air mixture (2025) is flowed to the fuelreformer (165) which decomposes the mixture (2025) forming a reformate,herein after called fuel (2027). The fuel (2027) is a reactant suitablefor chemical reaction with an anode surface of the SOFC stack. The fuel(2027) or reformate typically includes a mixture of H2, CO, CO2 and H20with traces of CH4 and other hydrocarbons. Other reformate contents mayinclude methane, ethane or ethylene. In an alternative embodiment thesupply fuel (8050) comprises primarily hydrogen (H₂) with little or noadditional components and a reformer (165) is not required. The fuelreceived from the fuel reformer or directly from the supply fuel sourcesis passed over the surface of the anode layer (150) for electro-chemicalreaction therewith.

A cathode gas input line (170) delivers gaseous or vaporous oxygen suchambient air or another oxygen source into the cold zone (110) e.g.through an intake fan or the like. An air delivery controller (198) incommunication with the electronic controller (190) is optionallydisposed along the air input line (170) in the cold zone to regulate airinput volume or mass flow rate as needed. The air input line (170)delivers room temperature air into a recuperator (175) which heats theinput air by a thermal energy exchange between hot gases exiting the hotzone and the incoming cooler air. The heated incoming air is passed overthe surface of the cathode layer (155) for chemical reaction therewith.

Both the spent fuel and oxygen diminished air exit the fuel cell stack(135) and mix in a combustion region or tail gas combustor (180). Themixture of unreacted fuel and unreacted air delivered into the tail gascombustor (180) spontaneously combusts therein locally generatingthermal energy. The combustor walls, detailed below, comprise materialshaving a high coefficient of thermal conductivity, e.g. between 100 and300 W/(m° K), and preferably above 200 W/(m° K). Additionally thecombustor walls are in thermal communication with the hot zone enclosurewalls (115) such that thermal energy generated by combustion inside thecombustor (180) heats the combustor walls to a high temperature whichquickly initiates thermal energy transfer to all regions of the hot zoneby conductive thermal energy transfer through the hot zone enclosurewalls (115).

Combustion byproduct exiting from the tail gas combustor (180)comprising hot gas is delivered into the recuperator (175). Therecuperator comprises a cross flow heat exchanger with counter flowconduits provided to transfer thermal energy from the combustion hotbyproduct to cooler incoming air to thereby heat the incoming air beforeit enters the SOFC fuel cell stack (135). After passing through therecuperator (175) the combustion byproduct is exhausted through anexhaust port (185).

A thermocouple or other temperature sensor (157) is affixed to a surfaceof the enclosure walls (115) to sense a temperature thereof and thetemperature information is communicated to the electronic controller(190). The controller (190) is in communication with other electronicelements such as one or more electrically operable gas flow valves, gasflow rate detectors and or modulators, associated with the supply fueldelivery controller (197), the air delivery controller (198) andelectrical power output detectors, or the like, and other elements asmay be required to control various operating parameters of the SOFC(100). The electronic controller (190) monitors DC current output aswell as temperature measured at the thermocouple and further operates tovary the supply fuel input and air flow rates as a means of controllingthe temperature. Additionally, an optional cold start module (195) maybe provided to preheat input supply fuel and/or air at start up. Thecold start module (195) may be a supply fuel igniter usable to ignite aportion of the supply fuel for preheating the enclosure walls and theSOFCs or the cold start module (195) may comprise an electrical heaterusable to preheat input fuel, or both.

4.4 EXEMPLARY HOT ZONE ARCHITECTURE

Turning now to FIG. 2 a first non-limiting exemplary embodiment of animproved SOFC system hot zone (2000), according to the presenttechnology, includes a SOFC fuel cell stack (2005) comprising aplurality of individual fuel cells enclosed within a hot zone cavity(2010). The hot zone cavity (2010) is surrounded by enclosure walls(2015) wherein the enclosure walls are formed from one or more ofcopper, molybdenum, aluminum copper, copper nickel alloys or acombination thereof. The enclosure walls are surrounded by a thermalinsulation layer (2012) which limits thermal energy from exiting the hotzone. An air gap (2155) is disposed between the hot zone enclosure walls(2015) and the thermal insulation layer (2012). The air gap (2155)provides a fluid flow conduit that leads to a hot zone exit port (2165)and is used to carry exhaust gases out of the hot zone.

The enclosure walls (2015) are configured to provide thermally conducingpathways comprising materials having a coefficient of thermalconductivity, of between 100 and 300 W/(m° K) and preferably more 200W/(m° K). Moreover, the thermally conducing pathways are disposed to actas thermal energy conduits suitable for conducting thermal energy fromhigh temperature areas of the hot zone to lower temperature areas of thehot zone in order to narrow the temperature differences of each area ofthe hot zone.

4.4.1 Reformer

The hot zone cavity (2010) of the present non-limiting exemplaryembodiment is a can-shaped cylindrical volume bounded by the hot zoneenclosure walls (2015) which include a side wall (2002) a top wall(2004) and a bottom wall (2006). The hot zone (2000) operates mostefficiently at a temperature above 350 or above 500° C. depending uponthe SOFC reactions being used and may be operated at temperatures in therange of 350 to 1200° C. Accordingly, each of the elements of the hotzone of the present technology is configured to operate reliably athighest temperatures expected for that element, e.g., 350° C. in somezones and up to 1200° C. inside the fuel reformer, e.g. proximate to thecatalytic reaction or inside the combustion regions.

According to a preferred non-limiting example embodiment of the presenttechnology a fuel reformer (2020) that uses an exothermic reaction toreform the supply fuel and air mixture (2025) is provided inside orpartially inside the hot zone to reform the supply fuel to generate fuel(2027) or reformate for delivery into each of the fuel cells of the fuelcell stack (2005). The reformer (2020) of the present exemplaryembodiment comprises a Catalytic Partial Oxidation (CPOX) reactor whichpartially combusts a supply fuel and air mixture (2025) deliveredthereto. The supply fuel reforming process creates a hydrogen rich fuel(2027), e.g., a reformate. The CPOX reactor includes a catalyzing medium(2040) such as a metallic or oxide phase of rhodium (Rh) or othersuitable catalyzers (e.g. Pt, Pd, Cu, Ni, Ru and Ce) coated on internalsurfaces thereof. The supply fuel and air mixture (2025) passing throughthe CPOX reactor is catalyzed as it passes over the catalyzing medium(2040) coated surfaces and the heat released by the reaction is radiatedand thermally conducted to the hot zone enclosure walls (2015) and helpsto heat the fuel cell stack.

The CPOX reformer (2020) comprises reformer enclosure walls (2030)surrounding a cylindrical catalyzing cavity (2035). The cylindricalcatalyzing cavity (2035) supports a catalyzing medium (2040) therein. Inthe present example embodiment, the catalyzing medium (2040) is a squarecell extruded monolith with exposed surfaces thereof coated with asuitable catalyst. The monolith is positioned such that the incomingsupply fuel and air mixture (2025) flows past the exposed surfaces ofthe square cell extruded monolith for catalyzation. Other suitablecatalyzing structures may include a plurality of parallel plate orconcentric ring structures or a porous metal or ceramic foam structuresuch as a sintered or extruded element formed with exposed surfacesthereof coated with the catalyzing agent. Alternately, the catalyzingstructure may comprise a plurality of mesh screens having exposedsurfaces coated with the catalyzing agent. The supply fuel and airmixture (2025) enters the reformer (2020) through a reformer input port(2045) and flows through the catalyzing medium (2040) for reforming bycontact with the catalyzed surfaces. The reformed fuel or reformate,herein after “fuel”, flows out of the reformer through a reformer exitport (2050) and into a fuel input manifold (2055).

In the present non-limiting exemplary embodiment, the reformer enclosurewalls (2030) comprises a cylindrical or square wall enclosing acylindrical or square cross sectioned catalyzing cavity (2035). Thecatalyzing medium (2040) is supported inside the catalyzing cavity(2035) disposed to force the incoming supply fuel and air mixture (2025)to flow through the catalyzing structure past the catalyzing surfaces. Athermal insulating element (2065) is disposed to surround outsidesurfaces of the catalyzing cavity (2035). The thermal insulating element(2065) is provided to limit thermal energy from entering or exiting thecatalyzing cavity (2035): The reformer enclosure walls (2030) maycomprise a high temperature steel alloy such as Inconel, a hightemperature copper alloy e.g. Monel or other suitable high temperaturematerial.

4.4.2 SOFC Fuel Cell Stack

The SOFC fuel cell stack (2005) is supported inside the can-shaped hotzone enclosure walls (2015). A plurality of rod shaped fuel cells (2080)is supported longitudinally inside a cathode chamber (2090). The cathodechamber (2090) is a cylindrical-shaped chamber bounded by the hot zoneenclosure side wall (2002) and by a pair of opposing disk-shaped top andbottom tube support walls (2070) and (2075). Each tube support wall(2070, 2075) is attached to the side wall (2002) by suitable attachingmeans such as by welding or brazing, by bracketing and mechanicalfastening or held in place without fasteners by a clamping force, or thelike. Preferably the fuel cell stack (2005) is assembled prior toinstallation into the hot zone enclosure walls (2015) and is removablefrom the hot zone enclosure walls (2015) as a unit, e.g. to repair orinspect the cell stack as needed. Accordingly, the top and bottom tubesupport walls (2070, 2075) may be captured in place between opposing endstops, not shown. The top tube support wall (2070) mechanically engageswith and fixedly supports a top or input end of each of the plurality ofrod shaped fuel cells (2080). The mechanical interface between the topsupport wall (2070) and each of the plurality of fuel cell input ends isa substantially gas tight interface in order to prevent the supply fueland air mixture (2025) in the fuel input manifold (2055) from enteringthe cathode chamber (2090). The top tube support wall (2070) ispreferably formed with Inconel. Additionally, each of the top end caps(2095) is also formed with Inconel, which is an effective material foravoiding creep in high temperature environments. The bottom tube supportwall (2075) mechanically engages with and movably supports a bottom oroutput end of each of the plurality of rod shaped fuel cells (2080). Inparticular the output end of each fuel cell (2080) is longitudinallymovable with respect to the bottom tube support wall (2075) in order toaccommodate changes in the length of each fuel cell as the fuel cellsare heated to an operating temperature between 350 and 1200° C. Anexample tube support system usable with the present technology isdisclosed by Palumbo in related U.S. patent application Ser. No.13/927,418, filed on Jun. 26, 2013 entitled, SOLID OXIDE FUEL CELL WITHFLEXIBLE ROD SUPPORT STRUCTURE.

Referring now to FIGS. 2 and 5C, the bottom tube support wall (2075)includes a disk shaped thermally conductive mass (2180) comprising oneor more materials having a coefficient of thermal conductivity, of morethan 100 W/(m° K) and preferably more than 200 W/(m° K) such as one ormore of copper, molybdenum, aluminum copper, copper nickel alloys or acombination thereof. The disk shaped thermally conductive mass (2180) isprotected by top and bottom protective surface layers (5045) and (5050)described below in relation to FIG. 5C. In one non-limiting exemplaryembodiment, each top (5045) and bottom (5050) protective surface layercomprises a separate disk shaped element in thermally conductive contactwith the disk shaped thermally conductive mass (2180). Specifically, thetop surface layer (5045) facing the cathode chamber (2090) comprises adisk-shaped chromium free high temperature metal alloy such as Monel andthe bottom surface layer (5050) that faces a combustion region (2135),or tail gas combustor, comprises a disk-shaped high temperature,corrosion resistant metal such a Hastelloy alloy.

Preferably, each of the top and bottom protective surface layers (5045)and (5050) is in thermally conductive contact with the thermallyconductive mass (2180) which is also in thermally conductive contactwith the hot zone enclosure cylindrical sidewall (2002). Accordingly asthe fuel air mixture is combusted in the tail gas combustor orcombustion region (2135) thermal energy generated by combustion isradiated to the walls enclosing the combustion region (2135) and fromthe enclosing walls is thermally conducted to the thermally conductivemass (2180) and to other regions of the hot zone through the hot zoneenclosure walls (2015). In addition, thermal energy emitted from thethermally conductive mass (2180) is radiated into the cathode chamber(2090) where it heats the cathode gas, or air flowing there through andheats surfaces of the fuel cells enclosed therein.

Each of the rod shaped fuel cells (2080) comprises a tube shaped annularwall (2085) wherein the anode layer is the support layer. The tubeshaped annular wall (2085) is open at both ends. The tube-shaped annularwall (2085) forms a fuel conduit that extends through the cathodechamber (2090) to carry fuel (2027) there through. Other rod shapesincluding square, triangular, pentagonal, hexagonal or the like, areusable without deviating from the present technology. Additionally,other support layers are usable to provide structural integrity. Eachfuel cell includes two metal end caps (2095) and (2100) or tube manifoldadaptors with one end cap attached to each of two opposing ends of thetube annular wall (2085).

Each end cap (2095) and (2100) or tube manifold adaptor comprises a cupshaped attaching end (2105) and a journal shaped supporting end (2110).The attaching end (2105) includes a blind hole sized to receive theoutside diameter of the annular wall (2085) therein. Each attaching end(2105) is fixedly attached to a rod end by a press or inference fit orby another fastening means such as brazing or an adhesive bond usingmaterials suitable for the operating temperature of the hot zone(350-1200° C.). The journal shaped supporting end (2110) includes anannular wall formed with an outside diameter sized to engage with acorresponding through hole passing through the top tube support wall(2070) on the input side and a corresponding through hole passingthrough the bottom tube support wall (2075) on the output side. Thejournal shaped supporting end (2110) further includes a through holepassing there through which serves as a cell input port (2115) at thetop end of the rod shaped fuel cell or as a cell output port (2120) atthe bottom end of the rod shaped fuel cell (2080). Preferably theendcaps (2095 & 2100) or tube manifold adaptors each comprise a hightemperature low Cr, corrosion resistant metal alloy thermally compatiblewith the fuel cell. The caps may be comprised of a ceramic coating onthe metal cap to prevent Cr contamination.

Referring to FIGS. 2 and 3, the top end cap (2095) of each fuel cell(2080) may provide electrical communication with an outside diameter orcathode layer of the annular wall (2085) such that the outside diameterof the annular wall (2085) is in electrical communication with one ofthe DC current output terminals (140) over an electrical lead (2125)through the end cap (2095). A second electrical lead (2130) is inelectrical communication with an inside diameter of the annular wall(2085) or anode layer and with a different terminal of the DC currentoutput terminals (140). Additionally electrical insulators (not shown)are provided between each end cap (2095) and (2100) and thecorresponding top and bottom tube support walls (2070) and (2075) toelectrically isolate the hot zone enclosure walls (2015) from electricalcurrent being generated by the fuel cell stack (2005).

Each rod shaped fuel cell is formed by the annular wall (2085) comprisesan anode support layer which is a structural anode material layer formedwith an inside and an outside diameter. The anode support layer maycomprise a cermat, as previously described. The outside diameter of theanode support layer annular wall (2085) is a least partially coated witha ceramic electrolyte layer such as a Yttria stabilized zirconia or acerium (Ce) or lanthanum gallate based ceramic. The outside diameter ofthe ceramic electrolyte layer is at least partially coated with acathode material layer such as lanthanum strontium cobalt oxide (LSC),lanthanum strontium cobalt oxide (LSCF), lanthanum strontium manganite(LSM) or the like.

In a second non-limiting example embodiment of the system hot zone(2000) the mechanical structure of the hot zone enclosure walls andinternal end walls is similar to that shown in FIG. 2 and describedabove however; the anode and cathode layers are on opposite sides of theceramic electrolyte layer. Specifically in the second embodiment theinside diameter of the anode support layer annular wall (2085), (asopposed to the outside diameter), is a least partially coated with aceramic electrolyte layer such as a Yttria stabilized zirconia or acerium (Ce) or lanthanum gallate based ceramic and the inside diameterof the ceramic electrolyte layer is at least partially coated with acathode material layer such as lanthanum strontium cobalt oxide (LSC),lanthanum strontium cobalt oxide (LSCF), lanthanum strontium manganite(LSM) or the like. In this example embodiment the anode support layer ofthe annular wall (2085) is an outside diameter of each fuel cell and theinside diameter of each fuel cell is the cathode layer. Thus in thesecond example embodiment the cathode chamber (2090) becomes an anodechamber and fuel is delivered into the anode chamber while the cathodegas, air is flowed through the rod shaped fuel cells.

The fuel 2027) is flowed over the anode material layer while the cathodegas, an oxygen-containing gas (e.g., air), is flowed over the cathodematerial layer in order to generate electrical current flow. The currentflow passes out of the cell stack over the electrical leads (2125) and(2130) to the DC current output terminals (140) and may be used to powerexternal devices. It is noted that in other embodiments such as thesecond embodiment briefly described above, the anode and cathodesurfaces can be reversed with the cathode layer on the inside diameterof the fuel cells and the anode layer on the outside diameter of thefuel cells and air flowing through the gas flow conduit formed by thefuel cells and fuel flowing over outside surface of the fuel cellswithout deviation from the present technology.

The fuel input manifold (2055) comprises a cylindrical chamber boundedby a disk-shaped top wall (2170) and the opposing disk-shaped top tubesupport wall (2070). The disk-shaped fuel input manifold top wall (2170)includes a thermally conductive mass (2160). The thermally conductivemass (2160) comprises one or more materials having a coefficient ofthermal conductivity of more than 100 W/(m° K) and preferably more than200 W/(m° K) such as one or more of copper, molybdenum, aluminum copper,copper nickel alloys or a combination thereof. The thermally conductivemass (2160) is in thermally conductive communication with the hot zoneenclosure walls (2015) and specifically with the side wall (2002). Thethermally conductive mass (2160) is positioned proximate to an annularcold start combustion chamber (2305), described below, in order toreceive thermal energy from fuel that is combusted within the annularcold start combustion chamber (2305) during startup and to thermallyconduct thermal energy received therefrom to the hot zone external walls(2015). Additionally, the thermally conductive mass (2160) radiatesthermal energy received from fuel combustion within the annular coldstart combustion chamber (2305) and received by thermal conductionthrough the hot zone enclosure walls to fuel (2027) as it passes throughthe fuel input manifold (2055).

The top tube support wall (2070) forms a gas tight seal with thejournal-shaped supporting ends (2110) of each of the fuel cell top endcaps (2095). Additionally each of the fuel cells (2080) is fixedly hungfrom the top tube support wall (2070) by the mechanical interface formedin the top tube support wall (2070) which includes through holes forreceiving the journal-shaped supporting ends (2110) or manifold adaptorsthere through. Additionally, the fuel input manifold (2055) is boundedby the side wall (2002).

Since the present exemplary embodiment utilizes a CPOX reformer (2002)which uses an exothermal reaction to reform supply fuel, the reformer(2020) is a thermal energy source which is beneficially disposed insidethe hot zone (2000) to heat incoming supply fuel and air mixture (2025)as the fuel enters the hot zone. However in other embodiments of SOFCsystems of the present technology the reformer (2020) may utilize anendothermic reaction, e.g. a steam reformer or a thermally neutralreaction e.g. an autothermal reformer to reform the fuel and in thesecases the reformer (2020) could be disposed outside the hot zone (2000)and placed instead in the cold zone (110), shown in FIG. 1. Thus, theimproved hot zone (2000) of the present technology can be operatedwithout a reformer (2020) without deviating from the present technology.

4.5 TAIL GAS COMBUSTOR

The tail gas combustor or combustion region (2135) is an annular volumedisposed between the disk shaped bottom tube support wall (2075), whichincludes a thermal mass (2180), both described above and shown in FIG. 2and a disk-shaped combustor end wall (2140) which also includes athermal mass (2175). Both thermal masses (2180) and (2175) comprise oneor more materials having a coefficient of thermal conductivity of morethan 100 W/(m° K) and preferably more than 200 W/(m° K) such as one ormore of copper, molybdenum, aluminum copper, copper nickel alloys or acombination thereof. The thermal masses (2180) and (2175) are positionedto receive thermal energy from the combustion region (2135) and areconfigured to conduct the thermal energy received from the combustionregion to the hot zone enclosure walls (2015) as well as to radiate thethermal energy received from the combustion region into the cathodechamber (2090) and the recuperator chamber (2210).

An annular combustor baffle (2185) is provided inside the annualcombustor region to redirect gas flow through the combustion region(2135) and create turbulence which increases convective energy transferto the side walls of the combustion region (2135). The combustor baffle(2185) may be fixedly attached to the hot zone enclosure side wall(2002) or may comprise a portion of a combustion chamber liner describedbelow.

A cathode feed tube (2145), described below, passes through thecombustion region (2135) along the central longitudinal axis (2060). Thewalls of the cathode feed tube (2145) are heated by convective thermalenergy transfer from combustion gases inside the combustion region(2135). Air flowing through the cathode feed tube (2145) toward thecathode chamber (2090) is heated by thermal energy radiated from thecathode feed tube (2145) to the air flowing there through.

Internal walls of the combustion region (2135) are lined with a hightemperature, corrosion resistant metal such a Hastelloy alloy. In thecase of the disk-shaped bottom tube support wall (2075), the surfacefacing the combustor region comprises Hastelloy. In the case of thecombustor region end wall (2140), the surface facing the combustorregion comprises Hastelloy. In each case the wall (2075) and (2140) isformed as a composite structure having a Hastelloy disk shaped liner inthermally conductive contact with the corresponding thermal mass (2180)and (2175) respectively. The side wall of the combustion region (2135)is also lined with a high temperature, corrosion resistant metal such aHastelloy. In one non-limiting example embodiment the sidewall linercomprises separate element formed as a tube shaped open endedcylindrical wall with the combustor baffle (2185) formed integraltherewith. Moreover the side wall liner is formed to be inserted intothe hot zone enclosure side wall (2002) and from either of its open endsand to make thermally conductive contact with the side wall (2002)substantially over the entire surface of the wall liner.

4.6 RECUPERATOR

Air (2200) enters the cathode feed tube (2145) through an input port(2205) and flows into a recuperator chamber (2210). The recuperatorchamber (2210) is positioned in close proximity to the tail gascombustion region (2135) in order to heat incoming air (2200) usingthermal energy generated by combustion of the spent fuel occurringinside the combustion region (2135). The recuperator chamber (2210) isan annular chamber surrounding the cathode feed tube (2145) and isbounded on a top side by the disk-shaped combustor end wall (2140), on abottom side by the disk shaped hot zone enclosure bottom wall (2006) andon its sides by the hot zone enclosure side wall (2002).

Thermal energy is conducted to walls of the recuperator chamber (2210)by the hot zone enclosure walls (2015), by the combustor end wall (2140)and to a lesser extent by the cathode feed tube (2145). Thermal energyis radiated from the recuperator chamber walls to the air (2200) as itpasses through the recuperator chamber (2210). Outside walls of therecuperator chamber (2210) are further heated by hot exhaust gassesexiting from the combustion region (2135). In particular the recuperatorchamber (2210) is surrounded by the air gap (2155) which carries hotexhaust gases exiting from the combustion region (2135) throughcombustor exit ports (2150) to the hot zone exit port (2165). Thermalenergy from hot exhaust gases heats outside wall portions of therecuperator chamber walls by convective heat transfer.

A recuperator baffle (2215) is disposed inside the recuperator chamber(2210) and passes through the cathode feed tube (2145) preventing airflow through the cathode feed tube (2145). Thus air (2200) entering thecathode feed tube (2145) through the input port (2205) impinges on therecuperator baffle (2215) inside the cathode feed tube and is forcedinto the recuperator chamber (2210) through one or more air input ports(2225). The input air (2200) flowing into the recuperator chamberthrough the air input ports (2225) passes around the recuperator baffle(2215) and reenters the cathode feed tube through one or morerecuperator air output ports (2235) after being heated in therecuperator chamber (2210).

4.7 COLD START COMBUSTOR

Referring to FIG. 2, the SOFC hot zone (2000) optionally includes a coldstart combustor (2300) provided to initially heat the hot zone to anoperating temperature above 350° C. or at least until spontaneouscombustion occurs in the tail gas combustor region. The cold startcombustor includes an annular startup combustion chamber (2305). Theannular startup combustion chamber (2305) surrounds the catalyzingcavity (2035) and the annular thermal insulating element (2065). Theannular startup combustion chamber (2305) is bounded on top by the diskshaped hot zone enclosure top wall (2004) and on bottom by thedisk-shaped fuel input manifold top wall (2170), which includes theannular thermal mass (2175). The annular startup combustion chamber(2305) is further bounded by the hot zone enclosure side wall (2002).

A startup combustor inlet port (2310) receives unreformed startup fuel(2315) therein from a startup fuel source, not shown. The startup fuel(2315) may comprise various combustible gaseous or vaporized liquidfuels such as natural gas, propane, methane, hydrogen, alcohols, or amixture of fuels and air. In some exemplary embodiments, the startupfuel (2315) includes the supply fuel and air mixture (2025). The startupfuel (2315) is delivered, along with air or another oxygen-containinggas, into the annular startup combustion chamber (2305) through thecombustor inlet port (2310) and is ignited by an electric spark igniter(2320) or some other ignition source.

During startup combustion, thermal energy generated by startup fuelcombustion inside the annular startup combustion chamber (2305) istransferred by convective thermal energy transfer to the hot zoneenclosure top wall (2004) and side wall (2002) as well as to the fuelinput manifold top wall (2170). From each of these walls the thermalenergy from startup combustion is conducted to other regions of the hotzone by the thermally conductive hot zone enclosure walls (2015).

Exhaust gases from the start up combustion exit the annular startupcombustion chamber (2305) through the startup combustor exit port (2325)which is in fluid communication with the air gap (2155) which leads tothe hot zone exit port (2165). Thus, the exhaust gases flowing from theannular startup combustion chamber (2305) to the hot zone exit port(2165) further heat external surfaces of the hot zone enclosure walls(2015) by convective heat transfer.

Internal walls of the annular startup combustion chamber (2305) arelined with a high temperature, corrosion resistant metal such Hastelloy.In the case of the disk shaped hot zone enclosure top wall (2004) thiswall is lined with a Hastelloy material layer on its inner surfacewherein the Hastelloy layer is in thermally conductive contact with thehot zone enclosure top wall (2004). In the case of the disk-shaped fuelinput manifold top wall (2170), a top side of this wall comprises aHastelloy material layer in thermally conductive contact with theannular thermally conductive mass (2175). In the case of the side wallsa cylindrical wall liner comprising a Hastelloy material is insertedinto the startup combustion chamber in thermally conductive contact withthe hot zone enclosure side wall (2002).

4.8 GAS FLOW DIAGRAMS 4.8.1 Fuel Flow Diagram

Referring now to FIG. 3 a schematic fuel flow diagram depicts the flowpath of the supply fuel and air mixture (2025) as it passes through thehot zone (2000). The supply fuel and air mixture (2025) enters thereformer input port (2045) and passes through the reformer catalyzingcavity (2035) to produce the fuel (2027), e.g., reformate (reformedfuel). The fuel (2027) exits the reformer through the reformer exit port(2050) and enters the fuel input manifold (2055). From the inputmanifold (2055), fuel enters each of the fuel cells (2080) throughcorresponding cell input ports (2115) and flows through each fuel celland exits the fuel cells through corresponding cell output ports (2120).Inside the fuel cell (2080) the fuel reacts on the anode material layerforming the inside surface of the cell annular walls (2085). Afterexiting the fuel cells through the cell exit ports (2120) the remainingfuel (2027), which comprises unreacted fuel and reaction by-productsenters the combustion region (2135) where it mixes with air exiting fromthe cathode chamber (2090) forming a mixture which is spontaneouslycombusted therein. As described above, thermal energy generated bycombustion in the combustion region (2135) is transferred to side wallsof the combustor region by radiation and convection and thermallyconducted to other regions of the hot zone through the hot zoneenclosure walls (2015). Additionally thermal energy generated bycombustion in the combustion region (2135) may be transfer to each ofthe thermally conductive masses (2175) and (2180) proximate to thecombustor region by gas to surface thermal transfer by convection andthermal conduction through the enclosure walls. Additionally, thethermally conductive masses (2175) and (2180) proximate to the combustorregion respectively radiate thermal energy into the recuperator chamber(2210) and the cathode chamber (2090) to heat air passing there through.

After combustion exhaust gases from the combusted mixture (shown asdashed arrows) exit the combustion region (2135) through one or morecombustor exit ports (2150) to the air gap (2155). From the air gap(2155) the exhaust gas from the combusted mixture exit the hot zonethrough a hot zone exit port (2165).

4.8.2 Fuel Flow Diagram Cold Start

As further shown in FIG. 3, startup fuel (2315) and air enters theannular startup combustion chamber (2305) through the startup combustorinlet port (2310) where the startup fuel is combusted.

After combustion exhaust gases (shown as dashed arrows) exit thecombustion region (2135) through one or more startup combustor exitports (2325) to the air gap (2155). From the air gap (2155) the exhaustgas from the startup combustor exit the hot zone through a hot zone exitport (2165).

4.8.3 Air Flow Diagram

Referring now to FIG. 4 a schematic air flow diagram depicts the flowpath of air (2200) as it passes through the hot zone (2000). The air(2200) enters the cathode feed tube (2145) through an air input port(2205). The air (2200) exits the cathode feed tube through a recuperatorair input port (2230) to enter the recuperator chamber (2210). Air flowsaround the recuperator baffle (2215) and reenters the cathode feed tube(2145) through a recuperator air output port (2235). Inside therecuperator chamber (2210) the air (2200) is heated by thermal energyradiated from the recuperator chamber walls (2006), (2002) and thecombustor end wall (2140) and associated the annular thermallyconductive mass (2175).

The air (2200) passes through the combustion region (2135) as it flowsthrough cathode feed tube (2145). In the combustion region the air isfurther heated by thermal energy radiating from surfaces of the cathodefeed tube (2145) before entering the cathode chamber (2090) while stillflowing through the cathode feed tube (2145). The air (2200) exits thecathode feed tube and enters the cathode chamber (2090) through aplurality of cathode chamber air input ports (2240) disposed along aportion of the length of the cathode feed tube (2145) that extends intothe cathode chamber (2090).

Once inside the cathode chamber (2090) the air (2200) fills the cathodechamber and impinges on the outside diameter or cathode layer of each ofthe fuel cells (2080) and reacts on the cathode material layer coatedover at least a portion of the outside diameter of each of the fuelcells. The reaction between air passing over the cathode material layercoupled with the reaction of fuel (2027) passing over the anode materiallayer forming the inside diameter of each of the fuel cells generates acurrent flow which is conveyed to the DC current output terminals (140)over the electrical leads (2125) and (2130) shown in FIG. 3.

After reacting with the cathode material layers coated on each of thefuel cells, the oxygen reduced air (2200), (shown as dashed flow lines)exits the cathode chamber (2090) through one or more cathode chamberoutput ports (2245) which lead into the combustion region (2135). In thecombustion region (2135) the oxygen depleted air mixes with unconsumedfuel (2027) exiting from the fuel cells and the mixture of is combusted.Exhaust gasses from the combusted mixture exit the combustion region(2135) through the combustor exit ports (2150) which lead to the air gap(2155). The air gap (2155) carries the exhaust gasses to the hot zoneexit port (2165) and out of the hot zone.

While FIG. 4 schematically shows two diametrically opposing recuperatorair input ports (2230), two diametrically opposing recuperator airoutput ports (2235) and pairs of two diametrically opposing cathodechamber air input ports (2240), however the actual device may includeany hole pattern having one or more holes arranged around thecircumference of the cathode feed tube (2145) as required for air flowdistribution. Similarly FIG. 4 shows two diametrically opposed cathodechamber air output ports (2245) and two diametrically opposing combustorexit ports (2150), however, the actual device may include any holepattern having one or more holes arranged around the circumference ofthe disk shaped wall (2004) or the side wall (2002) as may be requiredfor air flow distribution. Alternate any of the gas ports describedabove may have non-circular shapes e.g. square, rectangular, and oval orslotted without deviating from the present technology.

4.9 ENCLOSURE WALL SURFACE TREATMENTS

According to an aspect of the present technology no copper surface isexposed to oxygen/air in order to avoid oxidation damage to the copper.This includes all surfaces forming the entire fuel flow pathway and allsurfaces forming the entire airflow pathway since both the fuel and theair contain or could contain oxygen. Copper surfaces that may be exposedto fuel flow or to air flow are at least protected by a layer of nickelplating applied to a thickness of 0.0005 to 0.0015 inches, (12.5 to 38.1μm) by electro-deposition plating or the like. The thickness of thenickel plating is more than 100 times the normal thickness ofconventional nickel electro-deposition coatings and the thicker nickelcoating is used to substantially prevent oxygen diffusion through thenickel coating.

This aspect of the present technology is shown in FIG. 5A which depictsa non-limiting exemplary section view taken through any one of the hotzone enclosure walls (2015). The hot zone cavity wall section (5005)includes a copper core (5010) comprising copper having a thermalconductivity approximately ranging from 370 W/(m° K) at 500° C. and 332W/(m° K) at 1027° C. The copper core (5010) has a thickness in the rangeof 0.01-0.125 inches (0.25-3.2 mm) however other thicknesses are usablewithout deviating from the present technology. More generally the hotzone cavity wall thickness may increase or decrease as needed for aparticular application. Generally thicker enclosure walls e.g. up toabout 0.25 inches take longer to heat to a desired operating temperaturebut have the advantage that once heated to the operating temperature thethicker walls have a higher capacity for thermal conduction and are lessprone to thermal gradient formation and provide a longer operating lifethan thinner walls when surface oxidation is the failure mode simplybecause it takes long to for thicker walls oxidize to a degree that thewall becomes unusable.

The copper core (5010) includes two opposing surfaces forming inside andoutside surfaces of the enclosure wall and in a preferred embodimenteach of the inside and outside surfaces of the copper core (5010) iscompletely covered by electro-deposition nickel coating layers (5015) onthe inside surface and (5020) on the outside surface. Each nickelcoating layer is applied to a layer thickness of at least 0.0005 inches,(12.5 μm) which is suitably thick to prevent oxygen diffusion throughthe nickel coating layer. More generally a desired nickel coating layerthickness in the range of 0.0005 to 0.0015 (12.5 to 38.1 μm) providesadequate surface protection from oxidation for a product life of up toabout 40,000 hours and thicker nickel coatings are usable to increaseproduct life time without deviating from the present technology.Referring to FIG. 2 the wall section (5005) is at least representativeof outer walls of the hot zone enclosure walls (2015) including the sidewall (2002), the disk-shaped top wall (2004), the disk shaped bottomwall (2006) and may be representative of some walls of the reformerenclosure walls (2030).

According to an aspect of the present technology combustion chambersurfaces are lined with a high temperature, corrosion resistant metalsuch a Hastelloy alloy in order to protect internal surfaces of thecombustion chamber from surface damage from exposure to hightemperatures, combustion byproducts and corrosive elements. AlternateMonel or lnconel is usable without deviating from the presenttechnology.

This aspect of the present technology is shown in FIG. 5B which depictsa non-limiting exemplary section view (5025) taken through a combustionchamber side wall. The side wall section (5025) includes the copper core(5010) of the hot zone enclosure side wall (2002) and theelectro-deposition nickel coating layers (5015) and (5020) applied overopposing sides of the copper core as described above. Specifically, thesection view (5025) includes the same hot zone external wall (5005)shown in FIG. 5A. In addition, the combustion chamber side wall section(5025) further includes a Hastelloy alloy liner (5030) positioned toline the inside surface of the combustion chamber. Referring to FIG. 2the side wall section (5025) is at least representative of cylindricalouter wall of the annular tail gas combustion region (2135) and thecylindrical outer wall of the annular cold start combustion chamber(2305). The sidewall section (5025) shows the hot zone side wall (2002)protected by the Hastelloy alloy liner element (5030). In the specificexample of the tail gas combustion region (2135) the Hastelloy alloyliner element (5030) also includes the combustor baffle (2185) attachedthereto or formed integral therewith. However, except for the presenceof the combustor baffle (2185) the section (5025) is also representativeof the top and side walls of the annular cold start combustion chamber(2305).

Each of the combustion regions (2135) and (2305) is also lined by a pairof opposing disk shaped Hastelloy alloy liner elements positioned toline the inside top and the inside bottom surfaces of the combustorregion. In the case of the tail gas combustor region (2135) its chambertop wall is formed by the bottom tube support wall (2075) which includesa disk shaped Hastelloy alloy liner element (5050), shown in FIG. 5C.The liner element (5050) is disposed to face the inside of the annulartail gas combustion region or chamber (2135). The tail gas combustionregion bottom wall is formed by the combustor end wall (2140) which alsoincludes a disk shaped Hastelloy alloy liner (5060) facing the inside ofthe annular combustion region chamber (2135).

In the case of the annular cold start combustion chamber (2305) of thecold start combustor (2300) its top chamber wall is formed by the hotzone enclosure top wall (2004) which includes an annular shapedHastelloy alloy liner element (5030) in contact with the inside top wallof the annular cold start combustion chamber (2305). Specifically thehot zone enclosure top wall (2004), also the top wall of the annularcold start combustion chamber (2305) is detailed in the section view ofFIG. 5B which shows the copper core (5010) covered by electro-depositednickel layers (5015) on the inside surface and (5020) on the outsidesurface and includes a Hastelloy alloy liner element (5030) in contactwith the nickel layer (5015). While the section view (5025) isvertically oriented and includes the Hastelloy combustor baffle (2185)the section is the same as the top wall (2004) without the combustorbaffle (2185) and rotated to a horizontal orientation like the top wall(2004).

The bottom wall of the annular cold start combustion chamber (2305) isformed by the top wall of the fuel input manifold (2170). This wall alsoincludes an annular shaped Hastelloy alloy liner element (5060), similarto the one shown in FIG. 5B, in mating contact with the inside bottomwall of the annular cold start combustion chamber (2305).

According to an aspect of the present technology no incoming air (2200)is exposed to a surface that is formed from a material that includeschromium in order to avoid poisoning the cathode layer applied toexterior surfaces of the fuel cells (2080). This includes all surfacesforming the entire incoming air flow pathway which includes interiorsurfaces of the cathode feed tube (2145), the recuperator chamber(2210), the recuperator baffle (2215), exterior surfaces of the cathodefeed tube (2145), interior surfaces of the cathode chamber (2090) andelements housed within the cathode chamber including the fuel cell endcaps (2095) and (2100) and the top and bottom tube support walls (2070)and (2075).

In one non-limiting exemplary embodiment, the cathode feed tube (2145),the recuperator baffle (2215) and each of the bottom end caps (2100) areformed from a high temperature metal alloy that is chromium free andresistance to corrosion; e.g. a Monel alloy. Additionally at least abottom surface of the combustor end wall (2140) which forms a topsurface of the recuperator chamber (2210) is formed by or lined by aprotective element formed from a high temperature metal alloy that ischromium free and resistant to corrosion; e.g. a Monel alloy. Similarlyat least a top surface of the bottom tube support wall (2075) whichforms a bottom surface of the cathode chamber (2090) is formed by orlined by a protective element formed from a high temperature metal alloythat is chromium free and resistance to corrosion; e.g. a Monel.

Internal surfaces associated with incoming air flow that are coated withthe above descried electro-deposited nickel plating layer can be exposedto air flow without exposure to chromium. Nickel plated surfaces thatmay contact incoming air flow include the side wall (2002) which formsthe sidewall of each of the recuperator chamber (2210) and the cathodechamber (2090), and the disk shaped bottom wall (2006) which forms thebottom wall of the recuperator chamber (2210). The surfaces each have across-section (5005) shown in FIG. 5A. Additionally other surfacesinside the cathode chamber (2090) formed by chromium containingmaterials such as the top tube support wall (2070) and the top end caps(2095) which are each formed from Inconel are covered by a layer ofnickel plating applied to a thickness of 0.0005 to 0.0015 inches, (12.5to 38.1 μm) by electro-deposition plating or the like in order to avoidair contamination with chromium.

Referring now to FIG. 5C a detailed section view depicts a section(5040) taken through the bottom tube support wall (2075). The detailedsection view shows the thermally conductive mass (2180) which comprisesa copper mass having a thermal conductivity approximately ranging from370 W/(m° K) at 500° C. and 332 W/(m° K) at 1027° C. The copper mass(2180) has a thickness in the range of 0.01-0.375 inches (2.5-9.5 mm)however other thicknesses are usable without deviating from the presenttechnology. A top surface of the bottom tube support wall (2075) facesthe inside of the cathode chamber (2090) and is therefore lined with adisk shaped liner element (5045) formed from a high temperature metalalloy that is chromium free and resistant to corrosion; e.g. a Monelalloy in order to avoid contaminating the cathode gas with chromium. Abottom surface of the bottom tube support wall (2075) faces the tail gascombustion region (2135) and is lined with a disk-shaped liner (5050)formed from a Hastelloy alloy.

Referring now to FIG. 5D a non-limiting exemplary detailed section viewdepicts a section (5055) taken through the combustor end wall (2140).The detailed section shows the thermally conductive mass (2140) whichcomprises a copper mass having a thermal conductivity approximatelyranging from 370 W/(m° K) at 500° C. and 332 W/(m° K) at 1027° C. Thecopper mass (2175) has a thickness in the range of 0.01-0.375 inches(2.5-9.5 mm) however other thicknesses are usable without deviating fromthe present technology. A top surface of the wall (2140) faces theinside of the tail gas combustion region (2135) and is therefore linedwith an annular liner element (5060) formed from a solid Hastelloyalloy. A bottom surface of the wall (2140) faces the recuperator chamber(2210) and is lined with an annular liner (5065) formed from a hightemperature metal alloy that is chromium free and resistant tocorrosion; e.g. a Monel alloy.

Referring now to FIG. 5E a non-limiting exemplary detailed section viewdepicts a section (5070) taken through the fuel input manifold top wall(2170). The detail section view shows the thermally conductive mass(2160) which comprises a copper mass having a thermal conductivityapproximately ranging from 370 W/(m° K) at 500° C. and 332 W/(m° K) at1027° C. The thermally conductive copper mass (2160) has a thickness inthe range of 0.01-0.375 inches (2.5-9.5 mm) however other thicknessesare usable without deviating from the present technology. Opposing topand bottom surfaces of the thermally conductive copper mass (2160) areoptionally covered by a layer of nickel plating (5075) applied to athickness of 0.0005 to 0.0015 inches, (12.5 to 38.1 μm) byelectro-deposition plating or the like. The nickel plating is applied inorder to avoid contact between the supply fuel and air mixture (2025)and the thermally conductive copper mass (2160) to avoid oxidizing thecopper mass surfaces. A top surface of the fuel input manifold top wall(2170) faces the inside of the annular cold start combustion chamber(2305) and is therefore lined with an annular liner element (5080)formed from a solid Hastelloy alloy to protect the thermally conductivemass (2160) from thermal damage.

A further variation of the walls (2075) and (2180) shown in detail inFIGS. 5D and 5C is that both sides of the copper mass (2180) and (2175)are covered by a layer of nickel plating applied to a thickness of0.0005 to 0.0015 inches, (12.5 to 38.1 μm) by electro-deposition platingor the like as described above e.g. with respect to FIG. 5E. The nickelplating is included in order to avoid contact between supply fuel andair mixture (2025) and or air (2200) and the corresponding copper mass(2180) and (2175) so that oxidizing the copper mass surfaces is avoided.In cases where the Hastelloy elements (5050) and (5060) and the Monelelements (5045) and (5065) comprise separate liner elements, i.e. notintegrally formed with the copper mass (2180), the copper mass ispreferably nickel plated on both of its opposing surfaces (e.g. as shownin FIG. 5E). However, in other cases where the disk or annular shapedliner elements (5045), (5050), (5060), (5065) are integrally formed withthe copper mass (2180) and or (2175) nickel plating the copper mass maynot be needed.

Generally, Hastelloy and Monel elements described above are used toprotect various surfaces from damage or to avoid contaminating incomingair by contact with chromium containing surfaces such as Inconel orHastelloy surfaces. In one nonlimiting example embodiment one or moreprotective elements is fabricated separately from the hot zone enclosurewalls (2015) and installed in place at assembly such as by brazing aprotective material layer onto a surface being protected. In the examplecopper mass (2180, 2175) shown in FIGS. 5C and 5D the protective Moneland Hastelloy layers are brazed directly to opposing surfaces of thecopper mass without nickel plating the copper mass. Preferably thebrazing step substantially gas seals the copper mass preventing air orfuel from contacting and oxidizing surfaces of the copper mass.

In the example thermally conductive copper mass (2160) shown in FIG. 5Ethe protective Hastelloy layer is brazed directly to a nickel layer(5075) of one surface of the copper mass that is disposed inside thecombustion region (2135). In this non-limiting example embodiment, theHastelloy layer is installed to protect the copper mass surface fromdirect exposure to combustion and corrosive elements. On the opposingsurface, only a nickel plated protective layer (5075) is applied ontothe copper mass surface which is disposed inside the recuperator chamber(2210) since only a nickel layer is needed to protect the copper masssurface from oxidation by incoming air. In the example of FIG. 5E theHastelloy layer (5080) can be mechanically attached, e.g. by fastenersor clamped in place, without the need to gas seal the copper surfacesince the copper surface is already protected by the nickel layer (5075)disposed between the thermally conductive copper mass (2160) and theHastelloy layer (5080).

Thus as described above, and particularly with respect to FIGS. 5B, 5C,5D and 5E the Hastelloy and Monel elements may include a plurality ofseparate elements such as disk shaped elements (5040), (5050) (5060),(5065) (5080) in mating contact with disk shaped thermal mass elements(2180), (2175), (2160) or the Hastelloy and Monel elements may includecylindrical wall portions e.g. (5030) disposed in mating contact withinternal cylindrical wall surfaces of combustion chambers such as theside wall (2002) of the hot zone enclosure walls. The cylindrical wallportions are inserted in appropriate positions inside the hot zoneenclosure walls, e.g. inside the annular cold start combustion chamber(2305) and inside the tail gas combustion region (2135) and brazed,welded or otherwise fastened or clamped in place in mating contact withsurfaces being protected. In some embodiments the Hastelloy and Monelelements may be applied directly to the conductive core surface (e.g.brazed directly onto a surface of the thermally conductive mass) with asubstantially gas tight seal. In other embodiments the thermallyconductive mass or core wall surface is nickel plated and the Hastelloyor Monel elements may be applied over the nickel plating without theneed to provide a substantially gas seal and instead of brazing over theentire surface to provide a gas seal the elements may be held in placeby clamping, by mechanical fasteners or by brazed or spot welded atselected points. In further embodiments any of the above described wallstructured may be formed as a metal casting with various protectivematerial layers formed on selected surfaces of the metal casting bywell-known methods including plating, sputtering, spray coating hotdipping or the like.

However, in other non-limiting embodiments of the present technologyportions of the external and or internal walls of the hot zone enclosurewalls (2015) are formed from prefabricated multi-layered compositematerials. The composite materials including plate and or tubing stockfabricated with a plurality of dissimilar metals layers which are usableto form various hot zone enclosure walls described herein.

In a first step sheets of dissimilar metals are joined together by anextrusion or rolling process generally referred to as cladding. In anexample embodiment, referring to FIG. 5C, a composite sheet comprising acopper mass (2180), a Hastelloy alloy layer (5050) and a Monel alloylayer (5045) are roll welded to form the composite sheet. Once formed,the bottom tube support wall (2075) may be cut from the composite sheetand holes and other features added in secondary operations. The bottomtube support wall (2075) is then assembled to the hot zone enclosurewalls (2015) by brazing, welding, mechanical fastening, clamping, hightemperature adhesive bonding or the like. Additionally the wall (2140),shown in FIG. 5D, includes the same material layers as the bottom tubesupport wall (2075) shown in FIG. 5C only in reverse order, may be cutfrom the same composite sheet and holes and other features added insecondary operations. Each of the wall (2140) and bottom tube supportwall (2075) is then assembled to the hot zone enclosure walls (2015) bybrazing, welding, mechanical fastening, clamping, high temperatureadhesive bonding or the like.

In an example embodiment, referring to FIG. 5E, a composite sheetcomprising a thermally conductive copper mass (2160) and a Hastelloyalloy layer (5080) are roll welded to form a composite sheet. In thisexample embodiment the nickel layer (5075) may be omitted such that thecomposite sheet has only two layers. Once formed, the fuel inputmanifold top wall (2170) may be cut from the composite sheet and holesand other features added in secondary operations. The fuel inputmanifold top wall (2170) is then assembled to the hot zone enclosurewalls (2015) by brazing, welding, mechanical fastening, clamping, hightemperature adhesive bonding or the like. In a further step thecomposite sheet may be nickel plated on at least the copper surface toprevent oxidation of the exposed copper surface.

Similarly referring to FIG. 5B, a two layer composite sheet comprising acopper core (5010) and a Hastelloy layer (5030) are roll welded to forma composite sheet. In this example embodiment the nickel layer (5015)and (5020) may be omitted such that the composite sheet has only twolayers. Once formed, holes and other features are formed by secondaryoperations and then the composite sheet is formed into a cylindricalwall. The cylindrical wall is cut to size and assembled with othercylindrical wall sections to form portions of the hot zone enclosureside wall (2002) associated with enclosing a combustion region. Thecylindrical wall portions may be joined together by brazing, welding,mechanical fastening, clamping, high temperature adhesive bonding or thelike. In a further step the composite sheet may be nickel plated on oneor both sides and the assembled host zone enclosure side wall may benickel plated to protect exposed copper surfaces from oxidation.

4.10 SOFC FUEL CELL STACK CONFIGURATIONS

Referring now to FIG. 6 portions of a non-limiting exemplary embodimentof a SOFC system embodiment (7000) usable with the present technologyare shown in a top section view. The configuration (7000) depicts acathode chamber (7010) enclosed by a circular hot zone enclosure wall(7015) shown in top section view. The circular enclosure wall (7015) issurrounded by a circular thermal insulation layer (7020) separated fromthe circular enclosure wall by a small air gap, not shown, usable as agas flow conduit as described above.

A cathode feed tube (7025) is shown centered with respect to thecircular hot zone enclosure wall (7015). A plurality of rod shaped fuelcells is disposed in two concentric circular patterns with each circularpattern centered with respect to the same center axes (7030). An innercircular pattern (7035) includes eight inner rod shaped fuel cells(7040). An outer circular pattern (7045) includes fourteen outer rodshaped fuel cells (7050). Other enclosure shapes and fuel cell patternsare usable without deviating from the present technology.

4.11 ALTERNATE SOFC SYSTEM EMBODIMENTS

Turning now to FIGS. 7-9 and 12-15, a first alternate non-limitingexemplary embodiment of a portion of an improved SOFC system (8000),shown in FIGS. 7A-9C, includes a U-shaped primary enclosure wallassembly (8045) enclosing SOFC stack (8005). A second alternatenon-limiting exemplary embodiment of a portion of an improved SOFCsystem is shown in FIGS. 12-13B. The second alternative SOFC systemincludes two L-shaped primary enclosure wall assemblies (12045) witheach L-shaped primary enclosure wall assembly (12045) enclosing a singleSOFC stack (8005) to provide a duel stack SOFC system (12000). A thirdalternate non-limiting exemplary embodiment of a portion of an improvedSOFC system (14000), is shown in FIG. 14. The third alternative SOFCsystem (14000) includes one L-shaped primary enclosure wall assembly(12045) enclosing a single SOFC stack (8005). A fourth alternatenon-limiting embodiment of a portion of an improved SOFC system (15000)is shown in FIG. 15. The fourth alternative SOFC system (15000) includestwo U-shaped primary enclosure wall assemblies (8045) each enclosing adifferent SOFC stack (8005). Each SOFC stack (8005) includes a pluralityof individual fuel cells (8010). In a non-limiting exemplary embodimentthe individual fuel cells (8010) are arranged in pairs of two individualfuel cells positioned side by side along a stack transverse width axis(y) as defined by a system coordinate axes diagram (8100) (shown inFIGS. 9A, 12 and 14). In the present embodiment, a plurality of pairs oftwo fuel cells (8010) are positioned side by side along a stacklongitudinal length axis (x). However, the technology described hereinis not limited to the exemplary arrangement of fuel cells in the presentembodiment and further is not limited to tubular fuel cells. Any othersuitable arrangement of fuel cells within an SOFC stack is usablewithout departing from the concepts of the technology described herein.The number of fuel cells (8010) in the SOFC stack is selected to meet apredefined electrical power generation demand or other stack capacityconsideration. In other embodiments the number of fuel cells arrangedalong either of the stack transverse width axis (y) or the stacklongitudinal length axis (x) can be one or more with the total number ofindividual fuel cells (8010) selected to meet a predefined electricalpower generation demand or other stack capacity consideration.

In a non-limiting exemplary embodiment, each fuel cell (8010) comprisesan open-ended hollow fluid conduit disposed along a conduit centralaxis. The shape of the hollow fluid conduit is preferably cylindrical oroval; however, other fluid conduit shapes such as square, rectangular,triangular, or other polygon, are usable without deviating from thepresent technology. Alternately, hollow fluid conduits can be arrangedin any embodiment that includes an anode layer separated from a cathodelayer by an electrolyte layer with an anode gas (e.g., reformate orsyngas) passing over the anode layer and a cathode gas (e.g. air)passing over the cathode layer without deviating from the presenttechnology.

Each fuel cell is formed by a perimeter wall surrounding the hollowfluid conduit. The perimeter wall comprises three primary materiallayers each shown schematically in FIG. 1. The three primary materiallayers include an anode layer or fuel electrode (150), a cathode layeror air electrode (155), and an electrolyte layer (145) separating theanode layer from the cathode layer. All the layers comprise solidmaterials, some of which (e.g., an anode) may include a solid materialformed with a porous structure. In the present non-limiting exemplaryembodiment, the perimeter wall includes an inside surface formed by theanode layer, an outside surface formed by the cathode layer and theelectrolyte layer disposed between the anode layer and the cathodelayer. Preferably one of the three layers is configured as a supportlayer, e.g. the anode layer, wherein the support layer is formed withenough structural stiffness and integrity to support each individualfuel cell (8010) in the operating position described below.

Referring to FIGS. 7A and 7B, each fuel cell (8010) includes a fuelinput end (8020) and a fuel output end (8025) corresponding withopposing open ends of the hollow fluid conduit. At least the fuel inputend (8020) is supported by an interface with a fuel input manifold(8015) or other support structure. In a non-limiting example, the fuelinput end (8020) of each fuel cell includes an end cap (2100) formed ascup shaped attaching end (2105) and a journal shaped supporting end(2110) configured to mechanically interface the fuel input end of eachfuel cell with a fuel input manifold (8015) such that the end cap (2100)couples the fuel input end with the fuel input manifold. Othermechanical interfaces of each fuel cell with a fuel input manifold(8015) are usable without deviating from the present technology. Themechanical interface of each fuel cell (8010) with the fuel inputmanifold (8015) is configured to fixedly support each individual fuelcell (8010) in an operating position wherein a central longitudinal axisof the hollow fluid conduit of each individual fuel cell (8010) issupported substantially parallel with the stack gas flow axis (z). Themechanical interface between the fuel input manifold and the fuel inputend (8020) of each individual fuel cell (8010) forms a gas tight seal.In a preferred embodiment, the fuel output end (8025) of fuel cell(8010) is unsupported; however, an upper support structure forsupporting the fuel output end (8025) of individual fuel cells (8010)with respect to the primary enclosure wall or other mechanical supportstructure is usable without deviating from the present technology.

As compared with the embodiments shown in FIG. 2 and described above,which delivers a flow of fuel (2027) into a top of the SOFC system and aflow of cathode air (2200) into a bottom of the SOFC system (2000), thefuel flow direction through the SOFC stacks shown in FIGS. 7A, 7B, 12,14, and 15 is reversed because the corresponding fuel input manifolds(8015) are near the base or bottom end of the corresponding SOFC systemswith only the bottom or fuel input end (8020) supported by the fuelinput manifold (8015) and the end caps (2100) or other couplingelements. Thus, according to an aspect of the present technology thefuel output end (8025) of the individual fuel cells is not supported ormechanically interfaced with other elements of the SOFC system. Thissupport structure is advantageous because it allows the fuel cells toexpand and contract longitudinally during thermal cycling, e.g. on-offcycling thereby avoiding stress in the fuel cells during thermalcycling. Additionally, this support structure is advantageous because itdoes not require a gas seal at the fuel output end (8025). Overall, thelack of output end support reduces cost and complexity while improvingreliability by eliminating potential system failure modes.

As shown in each of FIGS. 7A, 7B, 12, 14, and 15, the fuel output end(8025) of each individual fuel cell (8010) is positioned to expel spentfuel from the fuel output end (8025) to a combustion region (8030) afterthe fuel has passed through the hollow conduit and interacted with theanode layer that forms the inside surface of each hollow conduit. Asshown by the dashed fuel flow indicator lines and arrows of FIGS. 7A,7B, 12, 14, and 15, a supply of fuel exits from a fuel reactor or fuelreformer (8035), flows through a fuel delivery conduit (8040) to thefuel input manifold (8015) where the fuel flow is distributed from thefuel input manifold to the fuel input end (8020) of each individual fuelcell (8010).

The fuel reformer (8035) is described above as the fuel reformer (2020)shown in FIG. 2 and fuel reformer (165) shown in FIG. 1. Details of anon-limiting embodiment of the fuel reformer (8035) are disclosed inrelated U.S. patent application Ser. No. 15/287,402 filed on 16 Oct.2016 and published as U.S. Ser. No. 10/573,911B2 on 25 Feb. 2020. Whilepassing through each fuel cell, the fuel reacts with oxygen ions (O⁺)passed from the cathode layer to the anode layer and becomes depleted ofhydrogen (H²) and carbon monoxide (MO) in order to generate anelectrical current flow. The depleted or spent fuel exits from each fuelcell through the output end (8025) to mix with spent cathode air in thecombustion region (8030). Other fuel reformer configurations andoperating modes are usable without deviating from the presenttechnology.

The SOFC system (2000) shown in FIGS. 2-4, and described above isconfigured with individual fuel cell input ports or input ends (2125)positioned at the top of the SOFC stack and with the fuel cell outputports or output ends (2120) positioned at the bottom of the SOFC stack.The SOFC system (2000) also positions the fuel input manifold (2055)above the fuel cell input ports or input ends (2125). The SOFC system(2000) is also configured with an annular cold start combustion chamber(2305) surrounding the catalyzing cavity (2035) of the fuel reformer(2035). The SOFC system (2000) also positions the tail gas chamber(2135) and the recuperator chamber (2210) at the bottom of the SOFCstack to receive spent fuel from the fuel cell output ports or outputends (2120). The SOFC system (2000) receives incoming air (cathode gas)into the recuperator chamber (2210) from the air input ports (2225)situated at the bottom end of the SOFC system (2000) and expels exhaustgases from the recuperator chamber through the hot zone exit port(2165). As further shown in FIG. 2, a supply fuel and air mixture (2025)enters the SOFC system (2000) to the fuel reformer (2020) for steadystate operations and to the startup combustion chamber (2305) throughthe inlet port (2310), both of which are positioned at the top end ofthe SOFC stack.

According to an aspect of the present technology the alternative SOFCsystems (8000, 12000, 14000, 15000) described herein provide alternativegas flow patterns as compared to the gas flow characteristics of thesystem (2000) described above. Referring to FIGS. 7A, 9A, 12, 14 and 15,a supply fuel and air mixture (2025), is receiving into correspondingfuel reformers (8035) at the top of the SOFC system. From the fuelreformers, (8035) fuel (8150) is delivered to corresponding fuel inputmanifolds (8015) by a fuel delivery conduit (8040). In preferredembodiments, the fuel delivery conduits (8040) are housed inside anintermediate enclosure (9000) or an outer enclosure (16000) eachdescribed below.

As best shown in FIG. 9A, a startup fuel (8152) is delivered to a burnerassembly (8155) through a conduit (8145). The burner assembly extendsthrough corresponding combustion regions (8030) and injects the startupfuel (8152) into the combustion regions during cold start operations. Anignitor (8160) is positioned inside the combustion region to ignite fuelflow exiting from the burner assembly to initiate combustion inside thecorresponding combustion regions (8030). As shown in FIGS. 12 and 15,when the SOFC system is a duel stack system, these systems preferablyinclude a burner assembly (8155) and an ignitor (8160) provided in eachcombustion regions (8030). As detailed below, each burner assemblyincludes a startup up fuel conduit (8145) for receiving a startup fuel(8152) from a connection with the supply fuel input line (160) or from aseparate startup fuel source. Each fuel delivery conduit (8040) mayinclude one conduit segments connected to one or more startup upconduits (8145) for use during start up. The corresponding fuel deliveryconduits may include control elements, e.g. valves and valve actuatorelements operable by an electronic controller (190) to independentlymodulate fuel flow and or divert fuel from the fuel reformer (8035) toone or more fuel input manifolds (8015) and to divert supply fuel fromthe supply fuel input line (160) to one or more startup up conduits(8145) under control by the electronic controller (190).

4.12 ALTERNATE SOFC COLD START OPERATION

Referring to FIGS. 7A, 9A, 12, 14 and 15, cathode air is receiving intocorresponding recuperator chambers (9050) at the top of the SOFC systemthrough the cathode input port (9040) and exhaust gases are directed outof the hot zone exhaust conduit (9055) through the exhaust (9045) whichalso positioned at the top of the SOFC system. Accordingly, as bestshown in FIG. 16B, each of the alternate SOFC systems (8000, 12000,14000, 15000) of the present technology is configured with all input andoutlet gas ports extending from a top wall of the SOFC system.

The combustion region (8030) includes a burner element (8155), shown inFIG. 9A, through which a startup fuel is delivered, via startup fuelinput conduit (8145), during a cold start operation. The startup fuel isignited in the combustion region (8030), e.g. by an electrical ignitor(8160), to provide thermal energy for heating one or more primaryenclosure wall assemblies (e.g., (8045) or (12045)) during the coldstart operation. After the SOFC system is heated to an operatingtemperature that can support a SOFC reaction in the fuel cells, a fuelflow from the fuel reformer (8035) to the SOFC stack through the inputmanifold (8015) is started in order to initiate a SOFC reaction. Thestartup fuel can be a reformate generated by the fuel reformer e.g. whenthe fuel (8150) is delivered to the startup conduit (8145) as startupfuel (8052), supply fuel and air mixture (2025), or an alternate startupfuel (8152), e.g. propane or the like. Startup fuel can be deliveredfrom another source e.g. through an additional start up fuel conduit(16020) shown in FIG. 16A. In this embodiment, the startup input conduit(16020) is fluidly interfaced with one or more start up conduits (8145).An advantage of the configuration of the combustion region (8030) shownin FIGS. 7A, 7B, 12, 14, and 15 is that the combustion region (8030) isconfigured for two operating modes: a startup mode where fuel isdelivered to burner element (8155) or and steady state power generationmode where fuel (8150) is delivered into individual fuel cells from thefuel input manifold (8015) and spent fuel and spent cathode gas arecombusted in the combustion region (8030). In other embodiments andoperating modes, the fuel delivery conduit (8040) feeds each of thestartup conduits (8145) and the startup mode includes simultaneousdelivery of fuel (8150) to corresponding startup burner elements (8155)and fuel input manifold (8015). The functional combination of thecombustion region (8030) for startup and power generation isadvantageous because it reduces the overall volume of the SOFC systemand reduces part count and complexity, as well as directly heating theprimary enclosure wall assembly (8045) and (12045), described below, theincoming cathode air, and the fuel cells (8010) which are heated oninside surfaces by fuel flowing therethrough and heated on outsidesurfaces by cathode air flow, and by thermal energy being radiated andconvectively transferred from the primary enclosure wall assembly. Ascompared to embodiments shown in FIGS. 1 through 4, where the startupchamber (2035) more directly heats the fuel reformer and the incominganode gas configurations that include the combustion regions (8030)surrounded by a combustion wall portion more directly heat the primaryenclosure wall assembly (8045, 12045) which redistributes the thermalenergy absorbed from the combustion region (8030) to other regionsdistal from the combustion region by thermal conduction.

4.12.1 U-Shaped Primary Enclosure Wall Assembly

Referring to FIGS. 9A and 9C, an exemplary hot zone enclosure assembly(8042) is shown in a side isometric view. The hot zone enclosureassembly (8042) includes a U-shaped primary enclosure wall assembly(8045) that includes a combustion region wall (8060) formed with acylindrical radius and two opposing primary enclosure sidewalls (8065,8070) extending from edges of the combustion region wall (8060). Each ofthe sidewalls (8065, 8070) extends from the combustion region wall to alower volume (8142) of the cathode chamber e.g. below the cathodechamber input ports (8095) along an axis that is parallel with the gasflow axis (z). The hot zone enclosure assembly (8042) further includesthe fuel input manifold (8015), an optional hot zone enclosure base wall(8075) and two optional hot zone enclosure end walls (8080, 8085). TheU-shaped primary enclosure wall assembly (8045) defines a cathodechamber (8055) (shown in the section views of FIGS. 7A and 7B). Thecathode chamber (8055) encloses the SOFC stack (8005) and the combustionregion (8030) such that the cathode layer formed on outside surfaces ofeach individual fuel cell (8010) is exposed to the cathode chamber(8055). The cathode chamber (8055) is bounded by the U-shaped primaryenclosure wall assembly (8045), the fuel input manifold (8015) andoptionally by the hot zone enclosure base wall (8075) and optionally bythe hot zone enclosure end walls (8080, 8085).

The cathode chamber (8055) receives a continuous flow of heated cathodegas, in this case a heated air flow, from an external air flow source,e.g. the air delivery control system, (198) shown in FIG. 1. Thecombustion region (8030) forms an upper most volume of the cathodechamber (8055). A lower volume (8142) of the cathode chamber, proximateto fuel input ends (8020), receives heated air flow (cathode gas)through a plurality of cathode chamber input ports (8095) shown in FIG.9B. A middle volume (8140) of the cathode chamber extends from the lowervolume (8142) of the cathode chamber to the fuel output end (8025) ofeach individual fuel cell (8010). The heated cathode gas flow reactswith the cathode layer surface of each individual fuel cell (8010) asthe heated cathode gas flow passes over external surfaces of theindividual fuel cells.

A non-limiting exemplary embodiment of the U-shaped primary enclosurewall assembly (8045) includes a combustion region wall (8060) formed toenclose the combustion region (8030). The combustion region wall (8060)provides an upper boundary of the combustion region (8030) substantiallyalong the full length of the stack length axis (x) and may extendfurther beyond the full stack length. The U-shaped primary enclosurewall assembly (8045) further includes two opposing primary enclosureside walls (8065, 8070). Each primary enclosure side wall (8065, 8070)extends from the combustion region wall (8060) and is fixedly attachedthereto or integrally formed therewith. Preferably each primaryenclosure sidewall extends the length of the fuel cell stack (8005) fromthe open fuel output end (8025) to the fuel input end (8020) parallelwith the gas flow axis (z).

Together, the two opposing primary enclosure side walls (8065, 8070) andthe combustion region wall (8060) bound a top and opposing sides of thecathode chamber (8055) along the stack length axis (x), this is bestshown by the section view of FIG. 7B. Preferably the combustion regionwall (8060) and the enclosure side wall or walls (8065, 8070) are formedas a unitary element to promote thermal conduction throughout. However,when combustion region wall (8060) and enclosure side walls (8065, 8070)wall(s) are formed as individual wall elements, the individual elementsare joined in a manner that provides high thermal conductivity acrossthe joint boundary, e.g. using a joining material that has a coefficientof thermal conductivity between 100 and 300 W/m° K.

In a non-limiting exemplary first embodiment, shown in FIG. 9C, a hotzone enclosure assembly base wall (8075) is mechanically interfaced withbottom edges of each of the two opposing primary enclosure side walls(8065, 8070). The mechanical interface is a weld or solder interface;however, other mechanical interface elements are usable includingfasteners, interconnecting fastening elements, e.g. rivets, clips orinterlocking features formed integral with each of the two opposingprimary enclosure side walls (8065, 8070) and/or formed integral withthe hot zone enclosure base wall (8075), or the hot zone enclosure basewall (8075) can be formed integral with one of the two opposing primaryenclosure side walls (8065, 8070). In the non-limiting first embodimentof FIG. 9A the fuel input manifold (8015) can be mechanically interfacedwith the hot zone enclosure base wall (8075), e.g. by welding, brazing,soldering, or mechanical fasteners without necessarily being interfacedwith one or both of the two opposing primary enclosure side walls (8065,8070).

In a non-limiting second exemplary embodiment, shown in FIG. 7A, each ofthe two opposing primary enclosure assembly side walls (8065, 8070) isor can be mechanically interfaced with the fuel input manifold (8015)without a base wall (8075). The mechanical interface between each hotzone enclosure assembly side wall and the fuel input manifold is a weldor solder interface; however, other mechanical interface elements areusable including separate fasteners and/or fastening elements formedintegral with one or both of the two opposing primary enclosure assemblyside walls (8065, 8070) and/or formed integral with the fuel inputmanifold (8015) in a manner that provides the desired mechanicalinterface. In the non-limiting second embodiment of FIG. 7A the hot zoneenclosure base wall (8075) is optional when the fuel input manifold(8015) is configured as a lower boundary of the cathode chamber (8055)along the full length of the stack length axis (x) and in some casesfurther beyond the full stack length. Preferably, the mechanicalinterface between the two opposing primary enclosure assembly side walls(8065, 8070) and the fuel input manifold (8015) forms a gas seal orprovides a high impedance to gas flow at the lower boundary of thecathode chamber (8055) to prevent cathode air flow from escaping fromthe cathode chamber (8055) lower boundary.

4.12.2 Intermediate Enclosure

The hot zone enclosure wall assembly (8042) installs inside anintermediate enclosure (9000), shown in an isometric transparent view inFIG. 8A. The intermediate enclosure is or can be formed as a gas tightgas flow chamber comprising opposing intermediate enclosure top wall(9005) and intermediate enclosure bottom wall (9010), opposingintermediate enclosure side wall (9015) and intermediate enclosure sidewall (9020) and opposing intermediate enclosure end wall (9025) andintermediate enclosure end wall (9030). The intermediate enclosure(9000) includes a fuel access port (9035) for receiving the fueldelivery conduit (8040) there through, a cathode input port (9040) forreceiving a cathode air flow there through, and an hot zone exhaust port(9045) for expelling exhaust out therefrom. Each of the ports (9035),(9040) and (9045) passes through a wall of the intermediate enclosure asrequired to direct the appropriate gas flow interface. In a non-limitingexemplary embodiment, the fuel port passes through one of the side walls(9015, 9020) and each of the cathode gas input port (9040) and the hotzone exhaust port (9045) pass through the intermediate enclosure topwall (9005).

A recuperator chamber (9050) and an hot zone exhaust conduit (9055),shown in FIG. 7A, are each gas flow chambers formed inside theintermediate enclosure (9000) and together form a counter flow gas togas heat exchanger. The recuperator chamber (9050) receives incomingcathode air flow from a cathode air flow source, e.g. the air deliverycontrol element (198) shown in FIG. 1, through a cathode input port(9040). Inside the recuperator chamber (9050) the incoming cathode airflow, e.g. ambient temperature air, is heated by convection and byradiation being emitted from walls of the hot zone exhaust conduit(9055). The heated cathode air flow is forced through the recuperatorchamber (9050) and exits from the recuperator chamber to a cathode inputmanifold (9070) through a recuperator exit port (9065). The cathode airflow source includes a variable speed air moving device (e.g., a fan orblower) that can be controlled to increase or decrease the flow rate ofthe incoming cathode air flow in accordance with electrical outputdemands and other process control commands.

The hot zone exhaust conduit (9055) receives a hot gas mixture from thecombustion zone (8030) through a combustion exhaust port (9060). Insidethe hot zone exhaust conduit (9055), the hot gas mixture is cooled asenergy is convectively and radiatively transferred to the walls of thehot zone exhaust conduit (9055). The hot gas mixture is forced throughthe combustion exhaust channel (9060) and out of the SOFC system throughthe hot zone exhaust port (9045) by operation of the variable speed airmoving device (e.g., a fan or blower) that can be controlled to increaseor decrease the flow rate of the incoming cathode air flow.

In the non-limiting exemplary configuration of FIG. 7A, the recuperatorchamber (9050) is formed inside the hot zone exhaust conduit (9055) andthe two chambers share a common wall (9075). When high temperature gasmixture is forced from the combustion region (8030) into the hot zoneexhaust conduit (9055), the high temperature gas mixture transfersthermal energy to the shared wall (9075) by radiant emission andconvection. The shared wall (9075) then transfers thermal energy to thecathode air flow passing through the recuperator chamber (9050) byconvection and radiant emission therefrom. Other gas to gas heatexchange configurations including providing a plurality of heat exchangechambers connected in serial or in parallel are usable without deviatingfrom the present technology.

Each of the recuperator chamber (9050) and the hot zone exhaust conduit(9055) is preferably disposed along the length of the SOFC stack alongthe stack length axis (x). Each of the cathode input port (9040), and/orthe hot zone exhaust port (9045), and/or the combustion exhaust port(9060) can each be implemented as a single port, as a plurality of portse.g. spaced apart along the stack length axis (x), and/or a one or moreopenings disposed along the stack length axis (x), e.g. formed ascircular, slotted or other openings that provide gas flow passages.Alternately, each of the recuperator chamber (9050) and the hot zoneexhaust conduit (9055) can be implemented as a single recuperatorchamber and a single exhaust chamber extending along the stack lengthaxis (x) or as a plurality of separated recuperator and exhaust chambersdisposed along the stack length axis (x) in parallel, with each separatechamber provided with its own cathode input port (9040), and/or the hotzone exhaust port (9045).

In a preferred embodiment each wall portion of the intermediateenclosure (9000) is fabricated from ferritic stainless steel such asAlloy18 SR® Stainless Steel, e.g. distributed by Rolled Metal Products,of Alsip, TL, US. The Alloy18 SR® Stainless Steel is preferred becauseunder operating temperatures and conditions of the SOFC system (8000)the added aluminum content advantageously forms a surface layer ofaluminum oxide which prevents oxidation of exposed surfaces of theintermediate enclosure (9000) which further prevents chromium fromleaching from the Alloy 18 SR® Stainless Steel. In a non-limitingexample, the Alloy18 SR® Stainless Steel has the following chemicalcomposition in approximate weight percentage, carbon 0.015, chromium18.0, manganese 0.30, silicon 0.60, aluminum 2.0, titanium 0.25 with theremaining weight percentage iron. The Alloy18 SR® Stainless Steel has acoefficient of thermal conductivity of about 22.8 (W/m° K) and acoefficient of thermal expansion of 5.9×10⁻⁶ (Ft/Ft/° F.) or 10.1×10⁻⁶(m/m/° K). A preferred thickness of the Alloy18 SR® Stainless Steel, atleast for the surrounding intermediate enclosure walls (9005, 9010,9015, 9020, 9025, 9030), is 4 mm (0.16 inches); however, a thicknessrange of 0.127 mm to 8.0 mm (0.005 to 0.32 inches) is usable and maydepend on the shape and size of the intermediate enclosure (9000), theforming methods used to form the intermediate enclosure (9000), theavailability of standard rolled stock thickness, the desired operatinglife in hours, or the like, without deviating from the presenttechnology.

With respect to material selection, the walls surrounding intermediateenclosure walls (9005, 9010, 9015, 9020, 9025, 9030) may have differentthickness than the walls that form the hot zone exhaust conduit (9055),the recuperator chamber (9050), the baffle(s) (9080) and various ports(9040, 9045, 9060) since the wall thickness selection can depend on, awall operating temperature requirements, a desired operating life of theSOFC system, a thermal energy management demand and/or structural andfabrication technique differences from one SOFC system to another. In analternate exemplary embodiment, at least a portion of the walls of theintermediate enclosure (9000) can comprise a chromium free hightemperature metal alloy such as Monel which is a nickel-copper alloywith small addition of aluminum and titanium.

4.12.3 Cathode Input Manifold

Referring to FIGS. 7A, 8A, the intermediate enclosure (9000) is formedas a cathode gas flow chamber that includes the recuperator chamber(9050) and a cathode input manifold (9070). The cathode input manifoldreceives incoming cathode air flow from the recuperator chamber whichfills the cathode input manifold (9070). The hot zone enclosure assembly(8042) is installed inside the cathode input manifold (9070) and theU-shaped primary enclosure wall assembly (8045) separates the cathodeinput manifold from the cathode chamber (8055) except that cathode airflow can pass from the cathode input manifold to the cathode chamberthrough the plurality of cathode chamber input ports (8095) which arepositioned proximate to the open fuel input end (8020) of each of theplurality of SOFC fuel cells in order to direct cathode gas flow intothe bottom volume of the cathode chamber so that cathode gas flowsinside the cathode chamber passes over the full length of the cathode ofeach fuel cell along the gas flow axis (z). The cathode input manifold(9070) is bounded by inward facing surfaces of each of the intermediateenclosure bottom wall (9010), the intermediate enclosure side walls(9015, 9020), the intermediate enclosure end walls (9025, 9030), byoutward facing surface of the bottom wall (9059) of the hot zone exhaustconduit (9055), and by outward facing surfaces of the U-shaped primaryenclosure wall assembly (8045). The cathode input manifold (9070)receives heated cathode air flow from the recuperator exit port (9065).Inside the cathode input manifold (9070) the heated cathode air flow isfurther heated by radiation emitted from the U-shaped primary enclosurewall assembly (8045) and the intermediate enclosure walls, e.g. (9005,9010, 9015, 9020, 9025, 9030) shown in FIG. 8A as the heated cathode airflow received from the recuperator exit port (9065) and by convectiondue to movement of the cathode air flow through the cathode inputmanifold. Cathode air flow exits from the cathode input manifold (9070)and enters the cathode chamber (8055) through one or more cathodechamber input ports (8095) passing from the cathode input manifold(9070) to the lower volume (8142) of the cathode chamber (8055). In apreferred embodiment, a plurality of cathode chamber input ports (8095)pass through each of the primary enclosure sidewalls (8065, 8070)proximate to bottom edges thereof. Once inside the cathode chamber(8055) the preheated cathode air flows upward from the cathode chamberinput ports (8095) to the cathode chamber middle volume where thecathode air reacts with external surface of the fuel cells to promotethe SOFC reaction. The preheated cathode air then reaches the combustionregion (8030) where spent cathode air mixes with spent fuel and themixture is combusted.

The cathode air flow through the SOFC system (8000) is illustrated inFIG. 7A, as indicated by sold black lines with black arrow heads showingthe direction of the cathode air flow and its pathway. Input cathode airflow is received from an air delivery module (198) which includes avariable speed fan or other air moving device and a corresponding airflow rate delivery controller. Cathode air flow passes from the airdelivery module (198) to the cathode input port (9040) to therecuperator chamber (9050) and exits the recuperator chamber through therecuperator exit port (9065) to the cathode input manifold (9070). Fromthe cathode input manifold (9070) the air flow passes into the cathodechamber lower volume (8142), through the cathode flow passages (8095)before passing over the cathode electrode surfaces of each individualfuel cell (8010) and then mixing with spent fuel exiting from the fueloutput end (8025) of each individual fuel cell (8010). The spent fueland the spent cathode air combust inside the combustion region (8030)further heating the primary enclosure wall assembly (8045). Thecombusted hot gas mixture passes from the combustion region (8030) tothe hot zone exhaust conduit (9055) and through the combustion exhaustport (9060) and then flows out of the system through the hot zoneexhaust port (9045).

The fuel flow through the SOFC system is also illustrated in FIG. 7A,indicated by dashed black lines and arrow heads showing the direction ofthe fuel flow and its pathways. A hydrogen rich fuel supply mixed withair is received from a supply fuel deliver control system (197) whichincludes a variable speed fan, pressure regulator, atomizer or other gasor fluid flow rate regulator device and a corresponding fuel deliveryflow rate controller. The fuel flow passes from the fuel deliverycontrol system to the fuel reformer (8035) where the supply fuel isreformed to provide a fuel, usually a reformate comprising hydrogen,carbon monoxide, and carbon dioxide. The fuel flows from the fuelreformer (8035) to the fuel input manifold (8015) through the fueldelivery conduit (8040). Inside the fuel input manifold, the fuel isheated by radiation and convection as it flows past walls of the inputfuel manifold (8015). From the fuel input manifold (8015) the fuel flowsinto the hollow chamber of each individual fuel cell (8010) where itpasses over the anode electrode surfaces thereof to participate in theSOFC reaction. The fuel is exits each individual fuel cell through theopen output end (8025) to the combustion region (8030) where the spentfuel mixes with spent cathode air. The spent fuel and the spent cathodeair combust inside the combustion region (8030). The combusted hot gasmixture passes from the combustion region (8030) to the hot zone exhaustconduit (9055) through the combustion exhaust port (9060) and then flowsout of the system through the hot zone exhaust port (9045). Thermalenergy generated by combusting the spent syngas and spent cathode airmixture is transferred to inside surfaces of the U-shaped primaryenclosure wall assembly (8045). Both the fuel delivery control system(197) and the cathode air delivery module (198) are independentlyoperable to vary flow rates as required to adjust electrical currentoutput, e.g. by varying the fuel flow rate, or to adjust a stacktemperature, e.g. by varying the air flow rate.

4.12.4 Heat Flow and Gas Flow Diagrams

A thermal energy flow diagram shown in FIG. 7B depicts a non-limitingthermal energy transfer pattern enabled by the present technology. Solidblack lines with black arrow heads pointing inwardly from wall surfacestoward either a cathode or a fuel flow region represent radiant emissionfrom higher temperature wall surfaces to lower temperature gas flows orto lower temperature surfaces of other walls, e.g. walls of theintermediate enclosure (9000). While not indicated by flow arrows,convective heat flow from high temperature fluid/gas flows to lowertemperature fluid/gas regions takes place in each of the gas flows ashigh temperature gas volumes proximate to higher temperature wallsurfaces mixes with cooler gas volumes distal from high temperaturesurfaces. The flow of cathode gas is indicated by solid black lines withsolid black arrow heads. The flow of anode gas is indicated by dashedblack lines with solid black arrows. As noted above, each of the fuelflow and the cathode gas flow enters the cathode chamber (8055)proximate to the input end (8020) of each fuel cell and flows upwardtoward the combustion region (8030) where spent fuel gas and spentcathode gases are mixed and combusted before exiting from the cathodechamber to the recuperator chamber (9050) through the combustion exhaustport (9060). Additionally, dashed black lines with solid black arrowsshown inside the thermally a thermally conductive core (8200) of the ofthe U-shaped primary enclosure wall assembly (8045), described below,indicate the direction and pathways of thermal conduction alongthermally conductive pathway provided thereby. As shown, the directionof the thermal conduction provided by the thermally conductive core(8200) is from the high temperature combustion region wall portion(8060) toward distal ends of each of the sidewalls (8065, 8070).

Incoming cathode air flow enters the recuperator chamber (9050) atambient temperature and the temperature of the cathode air flow isincreased when the cathode air flow is heated by heat exchange betweenthe higher temperature shared wall (9075) and the lower temperatureincoming cathode air flow as indicated by arrow heads directed into therecuperator chamber (9050) from the shared wall (9075). Inside thecathode input manifold (9070) the temperature of the cathode air flow isfurther increased when the cathode air flow is heated by heat exchangebetween the higher temperature U-shaped primary enclosure wall assembly(8045) and the lower temperature cathode airflow as indicated by arrowheads directed from outside surfaces of the U-shaped primary enclosurewall assembly (8045) into the cathode input manifold (9070).Additionally, each of the intermediate enclosure walls (9005, 9010,9015, 9020, 9025, 9030) are heated by radiant emissions from the highertemperature U-shaped primary enclosure wall assembly (8045) and by heatexchange with the cathode air flow. The cathode air flow is furtherheated by heat exchange between the intermediate enclosure walls and thecathode air flow whenever the temperature of the intermediate enclosurewalls is higher than the temperature of the cathode air flow.Alternately, when the temperature of the intermediate enclosure walls isless than the temperature of the cathode air flow, e.g. during astart-up cycle, the intermediate enclosure walls are heated by heatexchange between the higher temperature cathode air flow and theintermediate enclosure walls.

Inside the cathode chamber (8055), the temperature of the cathode airflow is further increased by heat exchange between inner surfaces of theU-shaped primary enclosure wall assembly (8045), outer surfaces ofindividual fuel cells (8010), and surfaces of the input fuel manifold(8015) and the cathode air flow with the heat flow direction going fromthe higher temperature surfaces or higher temperature gas flow regionsto the lower temperature surfaces or gas flow regions, as indicated byarrow heads directed from the above listed surfaces and the cathode airflow. Thus, the temperature of the cathode air flow continuouslyincreases as it flows through the cathode chamber from the cathodechamber flow passages (8095) to the combustion region (8030).

In a non-limiting example operating mode, the temperature of the gasmixture in the combustion region (8030) and inside at least a portion ofthe anode surfaces inside the cells is at least 350° C. before a steadystate SOFC reaction and DC current output from the SOFC stack (8005) canbe maintained. Once a steady state SOFC reaction is established, thetemperature of the gas mixture in the combustion region (8030) canexceed 500° C. Accordingly, the gas mixture while passing from thecombustion region (8030) through the hot zone exhaust conduit (9055) tothe hot zone exhaust port (9045) has a temperature that is much higherthan the temperature of the incoming cathode air flow and higher thanthe surrounding walls of the hot zone exhaust conduit (9055). Thetemperature of the gas mixture therefore decreases while passing throughthe hot zone exhaust conduit (9055) as heat is transferred by heatexchange between the higher temperature exhaust gas and walls of the hotzone exhaust conduit (9055), including the shared wall (9075). Theheated walls of the hot zone exhaust conduit (9055), especially theshared wall (9075), which causes heat exchange to the cooler incomingcathode air as incoming cathode air flows through the recuperatorchamber (9050).

Referring again to FIG. 7B, incoming fuel air mixture enters the fuelreformer (8035) at ambient temperature and is heated by partialcombustion by the Catalytic Partial Oxidation (CPOX) reactor or fuelreformer (8035). During the CPOX reaction, the temperature of the fuelcan peak near 1200° C. Accordingly, the temperature of fuel exiting fromthe fuel reformer (8035) decreases as the fuel passes from the fuelreformer through the fuel conduit (8040) and the fuel input manifold(8015) and through each of the fuel cells from the fuel input end (8020)to the fuel output end (8025). Thus during steady state operation, aftera SOFC reaction that produces output current has been established, thetemperature of the fuel flow is likely continuously reduced along theflow path that extends from the fuel reformer (8035) to the input fuelmanifold (8015) and then may be increased or decreased as the fuel flowpasses from the input fuel manifold to the combustion region (8030) asheat flows from the fuel flow by heat exchange to the lower temperaturesurfaces of the surrounding fuel passageways including the walls of thefuel input manifold (8015) and the walls of the fuel cells (8010) whichincrease in temperature as a result of absorbing heat flow from the fuelflow. In some embodiments, the direction of heat exchange can change,e.g. when the temperature of the fuel flow becomes less that thetemperature of the inside walls of the fuel cells. As noted above, thetemperature of the gas mixture from the combustion region (8030)continues to decrease as it flows out of the SOFC system.

Referring again to FIG. 7B, dashed black lines with black arrows showthe direction and pathways of thermal energy transfer by thermalconduction from a high temperature region of the thermally conductivecore to a low temperature region of the thermally conductive core. Thethermally conductive core passively reduces a thermal gradient betweenthe core top portion (8215) and each of the core side walls (8205) and(8210). The core top portion bounds the combustion region (8030) whichas noted above has a temperature of at least 350° C. and reach up toabout 1200° C. The gas mixture inside the combustion region has a highertemperature than the surrounding surfaces such that heat flows from thegas mixture to the combustion region wall (8060) by forced heatconvention and the radiation absorbed by the combustion region wall istransferred to each of the sides walls (8065, 8075) by thermalconduction as will be described below.

4.12.5 U-Shaped Hot Zone Enclosure Assembly

Referring now to FIGS. 7A, 9A, 9B, and 9C, the hot zone enclosureassembly (8042) comprises the SOFC stack (8005), the fuel input manifold(8015) and the U-shaped primary enclosure wall assembly (8045).Optionally the hot zone enclosure assembly (8042) further includes thehot zone enclosure base wall (8075), a first hot zone enclosure end wall(8080), and a second hot zone enclosure end wall (8085). The U-shapedprimary enclosure wall assembly (8045) includes a combustion region wallportion (8060), a first primary enclosure side wall (8065) and a secondprimary enclosure side wall (8070) which are both joined with thecombustion region wall portion.

Each primary enclosure wall portion (8060), (8065) and (8070) includes athermally conductive core (8200) and the core is protected fromoxidation by outer layers applied to exposed surfaces thereof. Thethermally conductive core (8200) comprises one or more materials havinga coefficient of thermal conductivity that is greater than 100 W/(m° K)and preferably greater than 200 W/(m° K). In a non-limiting exemplaryembodiment, the one or more thermally conductive core materials comprisecopper, molybdenum, aluminum, beryllium, iridium, rhodium, silver,tungsten, or alloys or combinations therefore that can be fabricatedwith a desired thermal conductivity and that can reliably meet thestructural requirements at the hot zone operating temperatures. In apreferred embodiment, the thermally conductive core (8200) comprisescopper or a copper alloy having a thermal conductivity of 370 (W/m° K)at 500° C. and 332 (W/m° K) at 1027° C. as described above. Thethermally conductive core (8200) preferably has a thickness in the rangeof 0.127 to 3.2 mm, (0.005 to 0.125 inches); however, other thicknessese.g. 0.5 to 6.0 mm (0.02 to 0.24 inches) are usable without deviatingfrom the present technology. The core thickness can increase or decreaseas needed to meet design requirements. A thicker thermally conductivecore (8200) e.g. up to 6.0 mm (0.24 inches, or more) requires morethermal energy to heat the core material to a desired operatingtemperature; however, increasing the core thickness is beneficialbecause this increases the rate of thermal energy transfer from oneregion of the core to another which advantageously redistributes thermalenergy more rapidly. Other reasons to increase the core thickness wouldbe to conduct thermal energy over a longer distance or to achieve alonger operating life if surface oxidation is a likely failure mode. Aswill be recognized, the thicker the thermally conductive core (8200),the longer it takes for thicker walls to oxidize to a degree that thecore becomes unusable. Additionally, aluminum can be used as a corematerial in SOFC systems that can generate electrical power when theSOFC system capable of generating electrical power without subjectingthe core material to a temperature in excess of about 550° C.

The thermally conductive core (8200) is a passive element that emitsradiation and absorbs radiation in proportion to the fourth power ofabsolute temperature difference (in ° K) between the thermallyconductive core and its surroundings in accordance with standard blackbody principles. Additionally, thermal energy is transferred to and fromthe thermally conductive core by thermal conduction from other surfacesof the U-shaped primary enclosure wall assembly (8045) in thermallyconductive contact. Thermal energy is further transferred from oneregion of the thermally conductive core to another region of thethermally conductive core by conduction when there is a thermallyconductive pathway and a temperature difference between the regions.

In a first non-limiting exemplary embodiment, the thermally conductivecore (8200) is a unitary element shaped to enclose the SOFC stack (8005)and form the cathode chamber (8055) around the stack. The unitaryelement is formed from a flat sheet of the core material, describedabove, sized to include the three primary enclosure wall portions(8060), (8065) and (8070) and bent to form the U-shape core element(8200) shown in FIG. 9C. As will be recognized, the U-shape core element(8200) can be formed by a metal bending fixture configured to bend aflat metal sheet into the desired U-shape. Other shapes are usable, e.g.a rectangular shaped core element, without deviation from the presenttechnology.

In a second non-limiting exemplary embodiment, the thermally conductivecore (8200) comprises three separate core portions (8205, 8210, 8215)each comprising one or more of the core materials described above andeach having a wall thickness in the thickness range described above. Thethree separate core portions include two substantially identical sideportions (8205) and (8210) and a core top wall portion (8215). The coretop wall portion (8215) is formed with a cylindrical radius, or thelike, along the longitudinal length thereof, and each of the sideportions (8205) and (8210) is formed from a flat metal sheet. Thelongitudinal dimension along the stack length axis (x) is preferably thesame for all three separate core portions. The three separate coreportions (8205, 8210, 8215) are joined together e.g. by solder joints,by braze joints, by welded joints, and or by other mechanical joiningtechniques such as by rolling or pressing mating edges of each side wallwith corresponding mating edges of the core top wall portion (8215), bycladding sheets of dissimilar metal together along the joints betweenthe core portion mating edges, or by otherwise fastening the coreportion mating edges of each side wall with corresponding core portionedges of the core top portion (8215). Irrespective of the fastening orjoining method, the mechanical interface between the three separate coreportions provides a thermally conductive pathway passing between thecore top portion (8215) and each of the two side core portions (8205)and (8210), and preferably the thermally conductive pathway is along theentire longitudinal length and full thickness of the joined core wallportions.

To prevent oxidation of the thermally conductive core (8200), each ofthe core portions (8205, 8210, 8215) is protected by a protective layerapplied over or attached to exposed surfaces of the thermally conductivecore (8200). In a first non-limiting exemplary embodiment, theprotective layer comprises nickel plating applied by an electro-platingprocess to a thickness of at least 0.0005 inches and ranging up to 0.002inches or more. The nickel plating is applied in order to prevent oxygendiffusion there through at operating temperatures of 350 to 1200° C. Ina second non-limiting exemplary embodiment the protective layercomprises an anodized surface formed over exposed core materials. Theanodized surface may be formed in a preassembly controlledelectroplating or oxygen rich environment or the anodized surface may beformed by exposure of protective layer surfaces to oxygen, i.e. cathodeair flow, over time during operation of the SOFC system. In anon-limiting exemplary embodiment, the anodized surface is formeddirectly onto core material surfaces when the core material comprisesaluminum or an aluminum copper alloy. When the anodized surface isformed in a preassembly controlled environment by an electroplating oran oxygen rich anodizing process the desired thickness of the anodizedlayer is preferably 0.0005 inches but ranging up to about 0.002 inchesin some applications in order to prevent oxygen diffusion through theanodized surfaces at operating temperatures of 350 to 1200° C.Irrespective of the electro-plating process or other anodizing layerapplication type, the thickness of the protective layer will bedependent upon the desired operating life of the SOFC system or of thethermally conductive core, based on the average and/or peak operatingtemperatures proximate to the thermally conductive core and based on theoxidant concentrations and/or oxidation rate that the plating thicknesswill be exposed to.

In a third non-limiting exemplary embodiment, the protective layercomprises one or more metal sheets disposed in mating contact withexposed surfaces of each of the three core portions (8205), (8210) and(8215). The metal sheets can be applied directly to uncoated surfaces ofthe thermally conductive core or can be applied over electroplatedsurfaces of the thermally conductive core. However as noted above anelectroplated nickel layer can serve as the protective layer without themetal sheets. As shown in the exploded isometric view of FIG. 9C, aninner protective sheet metal layer (8220) is fabricated as a U-shapedstructure formed to attach to the inside surfaces of each of the threecore portions (8205), (8210), (8215) wherein the inside surfaces of theinner protective layer (8220) face the SOFC stack. Preferably, theoutside surfaces of the inner protective layer (8220), facing away fromthe SOFC stack, and the inside surfaces of the three core wall portions(8205, 8210, 8215) are in mating contact over the entire inside surfacearea of the three core wall portions. The inner protective layer (8220)can extend beyond portions of the U-shaped thermally conductive core(8200) e.g. when a longitudinal length of the inner protective layer(8220) along the stack longitudinal length axis (x) extends beyond thelongitudinal length of the thermally conductive core (8200) or when adimension of the inner protective layer along the gas flow axis (z) isgreater than the dimension of the thermally conductive core along thesame axis, e.g. as shown in FIG. 9C where a bottom edges (8240, 8245) ofinner protective layer (8220) each extends to mate with the hot zoneenclosure base wall (8075), or other mechanical interface surfaces suchas may be provided by the fuel input manifold (8015). Similarly, sideedges of the inner protective layer (8220) can extend beyond side edgesof all three core portions (8205), (8210), (8215) e.g. to mate with ahot zone enclosure end walls (8080) and (8085) and/or to extend thelength of the cathode chamber (8055) along the stack longitudinal axis(x). The inner protective layer (8220) includes an inner top portion(8225) formed with a cylindrical radius along the stack length axis (x)and two opposing inner side wall portions (8230) and (8235) eachextending from a different edge of the cylindrical radius of the innertop portion (8225).

Each of the inner protective layer side wall portions (8230) and (8235)is attached to the hot zone enclosure base wall (8075) e.g. by amechanical interface between the inner side wall bottom edges (8240) and(8245) and the primary enclosure base wall (8075) which are joined alongthe entire interface e.g. by welding, soldering, or other mechanicalinterfaces configured as a gas seal or to provide a high impedance togas flow. The hot zone enclosure base wall (8075) is also attached tothe intermediate enclosure (9000) at its bottom wall (9010) and/or theside and end walls (9015, 9020, 9025, 9030) such that the mechanicalinterface between the inner side wall bottom edges (8240) and (8245) andthe primary enclosure base wall fixedly supports the U-shaped primaryenclosure wall assembly (8045) inside the intermediate enclosure (9000).Alternately, each of the inner protective layer side wall portions(8230) and (8235) is directly attached to the intermediate enclosurebottom wall (9010) by a mechanical interface between the inner side wallbottom edges (8240) and (8245) and the intermediate enclosure bottomwall (9010), which are fixedly attached e.g. by welding, brazing,soldering, or other mechanical interfaces. Alternately, each of the sidewall portions (8230) and (8235) is attached to the fuel input manifold(8015) by a mechanical interface between the inner side wall bottomedges (8240) and (8245) and the fuel input manifold (8015), which arefixedly attached e.g. by welding, brazing, soldering, or othermechanical interfaces. In this embodiment the fuel input manifold (8015)is attached to the intermediate enclosure bottom wall (9010) or otherintermediate enclosure walls such that the mechanical interface betweenthe inner side wall bottom edges (8240) and (8245) and the fuel inputmanifold (8015) fixedly supports the U-shaped primary enclosure wallassembly (8045) inside the intermediate enclosure (9000). Irrespectiveof the attachment technique, the mechanical interface between the innerside wall bottom edges (8240) and (8245) and the hot zone enclosure basewall (8075), or between the inner side walls and the input fuel manifold(8015), or between the inner side walls and the intermediate enclosurebottom wall (9010), the mechanical interface preferably provides a gasseal or provides a high impedance to gas flow corresponding with a lowerboundary of the cathode chamber (8055). In a preferred embodiment, eachof the inner protective layer side wall portions (8230) and (8235)includes a plurality of cathode chamber input ports (8095) passingthrough an inner side wall portion that extends below bottom edges ofthe thermally conductive core side walls (8205) and (8210) proximate tothe bottom edges (8240) and (8245) thereof, and the input ports (8095)are disposed evenly spaced apart along the stack length axis (x). Theposition of the cathode chamber input ports (8095) along the gas flowaxis (z) is selected to deliver cathode air flow into the lower volume(8142) of the cathode chamber (8055) proximate to the fuel input end(8020). Alternate cathode chamber input port embodiments include asingle slotted opening and/or a plurality of apertures of variousopening shapes such as circular, oval, square, rectangular, or the like.Alternately, the cathode chamber input ports (8095) can pass through theinner side walls (8230, 8235) and the core side walls (8205, 8210) wheninside surfaces of the cathode chamber input ports (8095) are protectedfrom oxidation e.g. by electroplating or an insert configured to preventoxidation.

An outer protective layer (8250) comprises two substantially identicalouter side wall portions (8255) and (8260) and an outer top portion(8265). As shown in the exploded isometric view of FIG. 9C, the threeouter protective layer portions, when joined together with each other,and joined together with corresponding outer surfaces of the thermallyconductive core (8200) form a U-shaped sheet metal structure shaped toattach to and protect the outside surfaces of the thermally conductivecore (8200) from exposure to oxygen rich cathode air flow, e.g. flowingthrough the cathode air input manifold (9070). Preferably, the insidesurfaces of the outer protective layer (8250) are in mating contact withcorresponding outside surfaces of the thermally conductive core (8200)that face away from the SOFC stack. The outer protective layer top wallportion (8265) is formed with a cylindrical radius along the stacklength axis (x) wherein an inside radius of the cylindrical radius ofthe outer protective layer top wall portion (8260) is matched with anoutside radius of the cylindrical radius of the thermally conductivecore top portion (8215) such that when the inside and outside radii arejoined together they provide mating contact therebetween. Each of theouter protective layer side wall portions (8255) and (8260) are formedfrom a flat sheet metal blank cut with a height dimension along the gasflow axis (z) and a length dimension along the stack length axis (x).The height dimension of each side wall portion (8255, 8260) is selectedto position outer side wall bottom edges (8270) and (8275) below ormatched with corresponding bottom edges of the thermally conductive coresidewall portions (8205) and (8210). When the cathode flow passages(8095) only pass through the inner side walls, (8230, 8235) the heightdimension of the outside side walls (8255, 8260) is short enough toprevent the outside side walls from covering the cathode flow passages(8095). In other embodiments, the cathode flow passages (8095) can passthrough the outside side walls (8260, 8255), the core side walls (8205,8210), and the inner side walls (8230, 8235). Preferably, insidesurfaces of the outer side walls (8255, 8260) and outside surfaces ofthe core sidewalls (8205, 8210) are in mating contact after assembly.

In a preferred embodiment, each wall portion of the inner protectivelayer and of the outer protective layer is fabricated from ferriticsteel such as Alloy18 SR® Stainless Steel, e.g. distributed by RolledMetal Products, of Alsip, TL, U.S. The Alloy18 SR® Stainless Steel ispreferred because under operating temperatures and the oxygen richconditions of the SOFC system (8000) the added aluminum contentadvantageously forms a surface layer of aluminum oxide in response tooxygen exposure which prevents further oxidation of exposed surfaces ofthe inner protective layer and of the outer protective layer, andprevents chromium from leaching from the Alloy 18 SR® Stainless Steel. Apreferred thickness of the Alloy18 SR® Stainless Steel is 4 mm (0.16inches); however, a thickness range of 0.13 to 6.0 mm (0.005 to 0.24inches) is usable and may depend on the shape and size of the innerprotective layer and the outer protective layer, the forming methodsused to form the inner and outer protective layers, the availability ofstandard rolled stock thickness, the desired operating life in hours, orthe like, without deviating from the present technology. In an alternateexemplary embodiment, the inner protective layer and the outerprotective layer at least in part comprise a chromium-free hightemperature metal alloy such as Monel which is a nickel-copper alloywith small addition of aluminum and titanium. A preferred thickness ofeach wall portion is approximately 4 mm (0.16 inches); however, theactual thickness can range between 0.13 to 6.0 mm (0.005 to 0.24 inches)without deviating from the present technology.

The hot zone enclosure base wall (8075) and each of the hot zoneenclosure end walls (8080, 8085) can each optionally include a thermallyconductive core portion (8200) and two protective layer portionsincluding an inner protective layer (8280) and an outer protective layer(8285), e.g. as depicted in section view in FIG. 8B. As with otherprotective layers described herein, the inner and outer protectivelayers (8280, 8285) can comprise nickel plating applied to exposedsurfaces of the thermally conductive core or the thermally conductivelayer can be protected by inner and outer protective layers like thesidewalls (8230, 8235, 8255, 8260) described above that are configuredto form an anodized layer either prior to assembly or formed by exposureto cathode air during operation of the SOFC system. As noted above,surfaces of the thermally conductive core (8200) are protected by anelectro-plating process wherein nickel is applied to a thickness of atleast 0.0005 inches and ranging up to 0.002 inches or more and/or byattachment of sheet metal forms comprising the Alloy18 SR® StainlessSteel with a thickness of 4 mm (0.16 inches) or a thickness range ofrange of 0.13 to 6.0 mm (0.005 to 0.24 inches).

The thermally conductive core portions (8200) and protective layerportions (8280) and (8285) are configured like the primary enclosurewalls (8060), (8065) and (8070) described above wherein the thermallyconductive core portion (8200) is protected from oxidation by twoprotective layer portions (8280) and (8285). The thermally conductivecore portion (8200) comprises one or more materials having a coefficientof thermal conductivity that is greater than 100 W/(m° K) and preferablygreater than 200 W/(m° K).

More generally each of the above described protective layers (8250,8220), shown in FIG. 9C and (8280, 8285), shown in FIG. 8B as well asthe nickel plating and/or an anodized layer applied by anelectro-plating process, is selected to provide a stabilized protectiveouter layer that prevents oxygen from diffusing through the stabilizedprotective outer layer. Preferably the stabilized protective layer doesnot include chromium; however, the stabilized protective layerpreferably prevents chromium from leaching through the stabilizedprotective layer. Example stabilized protective outer layer materialsinclude aluminum oxide, titanium oxide, or other suitable oxide orpassivation layers.

The hot zone enclosure assembly (8042) shown in FIG. 9A is equipped witha startup fuel input conduit (8145) in fluid communication with a fueldelivery control module (197) shown in FIG. 1 for delivering a startupfuel flow (8152) into the startup fuel input conduit (8145) which is influid communication with a burner element (8155) passing through thecombustion region (8030). A fuel ignitor element (8160), shown in FIG.7A, extends into the combustion region (8030) and is used to ignite thestartup fuel flow (8152) as it exits from the burner element (8155)inside the combustion region during a cold start cycle to rapidlyincrease the temperature of the U-shaped primary enclosure wall assembly(8045) and the SOFC stack (8005). The startup fuel flow (8152) comprisesa mixture of hydrogen rich fuel and air that has not been reformed or anunreformed hydrocarbon rich gas such as propane. During a cold start ofthe SOFC system, the fuel delivery control module (197) can deliverstartup fuel flow (8152) directly into the burner element (8155) andignite the fuel exiting from the burner element (8155) using the ignitorelement (8160). Additionally, the air delivery module (198) shown inFIG. 1 can deliver an air flow into the recuperator chamber (9050) to beheated before passing through the cathode input manifold (9070) and thecathode chamber (8055) and then to the combustion region (8030). Whenthe U-shaped primary enclosure wall assembly (8045) and the SOFC stack(8005) reach a predetermined start up temperature, the fuel deliverycontrol module can deliver startup fuel flow (8152) into the burnerelement (8155) and supply fuel flow (8050) the fuel reformer (8035) toinitiate a flow of fuel (8150) through the SOFC stack (8005) while aheated air flow is moved through the cathode chamber to eventuallyinitiate a SOFC reaction.

4.12.5.1 Enclosure Wall Assembly Fabrication Processes

In a first non-limiting exemplary fabrication process, each of the innerprotective layer (8220) and the thermally conductive core (8200) isformed as a unitary flat sheet from the appropriate material describedabove. Each flat sheet is cut to predetermined finished dimensionscorresponding with the final dimensions of the inner protective layerand the thermally conductive core. Any additional processing for eithersheet is preferably completed while the unitary flat sheet is still aflat sheet. The additional processing at least includes drilling,punching, or otherwise forming the cathode chamber input ports (8095)that pass through the inner protective layer (8220) (or the innerprotective layer and the core) and adding other holes or formed featuresas may be required to provide mechanical interface elements used toattach the inner protective layer bottom edges (8240, 8245) with the hotzone enclosure base wall (8075), or to attach the inner protective layerbottom edges (8240, 8245) with the input fuel manifold (8015) and/or toattach the inner protective layer bottom edges (8240, 8245) to theintermediate enclosure (9000). Additional holes or features as may berequired to provide other mechanical interface features such as forattaching the inner protective layer (8220) to the hot zone enclosureend walls (8080, 8085) or for attaching the inner protective layer(8220) or the outer protective layer (8250), to the thermally conductivecore (8200) or for providing fuel or cathode air flow ports, e.g. thecombustion exhaust port (9060), or providing access for the fueldelivery conduit (8040), or for providing a fuel conduit to thecombustion region for use during cold start-up, or for providing accessfor electrical interfaces for sensor attachment points, or the like, arealso added before assembling the U-shaped primary enclosure wallassembly (8045).

After preparing the flat sheets for assembly, including electroplating,machining, punching etc., the inner protective layer (8220) and thethermally conductive core (8200) are joined together in the flat e.g. byaligning and clamping the two sheets in mating contact with each otherand joining the two sheets together to form a composite sheet metalstructure which is still a flat sheet. The joining technique may includewelding, brazing, soldering, fastening, e.g. riveting, self-riveting orself-clinching, by folded tab joints or the like.

In the case where either of the sheet materials is a rolled sheet, thegrain direction runs parallel to the rolling direction. Thus, therolling direction of each sheet should be identified before cutting andassembling the sheets together and consideration should be given toorienting the grain direction with respect to a bending axis if thesheets will be bent. Additionally, the grain direction of the thermallyconductive core can have a different coefficient of thermal conductivitywith respect to other axes of the core sheet material. Accordingly, thethermally conductive core should be oriented with the highest thermalconductivity axis directed from the core top portion (8215) to thebottom edges of the core sidewalls (8205, 8210).

The composite sheet, comprising the thermally conductive core (8200) andthe inner protective layer (8220) joined together in mating contact, isthen bent to form the U-shaped structure shown in FIG. 9C with the innerprotective layer positioned to face the SOFC stack. The cylindricalradius has a longitudinal axis along the stack length axis (x). In anon-limiting exemplary embodiment, the bend radius is formed by ahydraulic bending device operable to bend or form the composite sheetmetal structure at room temperature (air bending) on a press break, orthe like. A bend radius that can be bent without damaging the materialsand managing undesirable consequences, such as spring back, isinfluenced by the material properties, e.g. hardness, tensile strength,the material thicknesses, the material grain direction, or the like andthese properties are taken into consideration when determining thefabrication process of different embodiments of the U-shaped primaryenclosure wall assembly (8045). Generally, it is preferable to bend thematerial transverse to the material grain direction to avoid materialcracking and separation of the joined material layers; however, thisvaries with material thickness. The composite sheet metal structure canbe preheated prior to bending, e.g. to 90 to 150° to reduce local stressduring bending, thereby helping to prevent material separation and/orundesirable deformation. Other forming methods such as forging at highertemperatures are usable without deviating from the technology.

In the first non-limiting exemplary fabrication process, outerprotective layer (8250) is formed from three separate flat sheets of theappropriate sheet material described above. The three separate flatsheets correspond with the outer top portion (8265) and each of the twoouter side portions (8255) and (8260). Each flat sheet is cut topredetermined finished dimensions corresponding with the finaldimensions of the U-shaped primary enclosure wall assembly (8045). Anyadditional processing for each of the three flat sheets is completedwhile the sheets are still a flat sheet and may be processed before thesheets are cut to the final dimensions. The additional processing mayinclude drilling, punching or otherwise forming passages for providingfuel or cathode air flow ports, e.g. the combustion exhaust port (9060)or a passage for providing access for a fuel delivery conduit into thecombustion region for use during a cold startup, or for providing accessfor electrical interfaces for current collection, sensor attachmentpoints, or the like. Additional holes or features as may be required toprovide other mechanical interface features such as for attaching theouter protective layer elements (8265, 8255, 8260) with the thermallyconductive core (8200), and/or with the hot zone enclosure end walls(8080, 8085) or for attaching the outer protective layers with the innerprotective layers as may be required, are added at this point in thefabrication process.

After preparing the flat sheets for assembly, including electroplating,machining, punching etc., the outer top portion (8265) is bent to formthe U-shaped structure shown in FIG. 9C with the inside radius of theouter top portion positioned to face the SOFC stack. The cylindricalradius has a longitudinal axis along the stack length axis (x) and hasan inside radius that matches with the outside radius of the core topportion (8215). The bend radius is formed by a hydraulic bending deviceoperable to bend or form the flat sheet metal structure at roomtemperature (air bending) on a press break, or the like. A bend radiusthat can be bent without damaging the materials and managing undesirableconsequences, such as spring back, is influenced by the materialproperties, e.g. hardness, tensile strength, the material thicknesses,the material grain direction, or the like and these properties are takeninto consideration when determining the fabrication process of differentembodiments of the outer top portion (8265). Generally, it is preferableto bend the material transverse to the material grain direction to avoidmaterial cracking and separation of the joined material layers; however,this varies with material thickness. The composite sheet metal structurecan be preheated prior to bending, e.g. to 90 to 150° to reduce localstress during bending, thereby helping to prevent material separationand/or undesirable deformation. Other forming methods such as forging athigher temperatures are usable without deviating from the subjecttechnology.

After preparing the two flat sheets (8255, 8260) and the bent outer topportion (8265) for assembly, including machining, punching etc., each ofthe three outer protective layers is assembled to outside surfaces ofthe thermally conductive core (8200) and joined to the thermallyconductive core. The joining technique may include welding, brazing,soldering, fastening, e.g. riveting, self-riveting or self-clinching, byfolded tab joints or a combination thereof. As noted above the threeouter protective layers are assembled to completely cover outsidesurfaces of the thermally conductive core (8200) to prevent oxidation bycathode air flow and or the mixture of spent cathode gas and spentsyngas in the combustion region (8030).

4.12.5.2 Fabrication Process: Three Sheets Joined Together

In a second non-limiting exemplary fabrication process, each of theinner protective layer (8220), the thermally conductive core (8200), andthe outer protective layer (8250) are formed as a unitary flat sheetfrom the appropriate sheet material thereof as described above. Eachflat sheet is cut to predetermined finished dimensions correspondingwith the final dimensions of the U-shaped primary enclosure wallassembly (8045). Any additional processing for each of the three unitaryflat sheets is completed while the unitary flat sheets are still flatsheets. The additional processing at least includes drilling, punching,or otherwise forming the cathode chamber input ports (8095) that passthrough the inner protective layer (8220) and adding other holes orformed features as may be required to provide mechanical interfaceelements used to attach the inner protective layer bottom edges (8240,8245) with the hot zone enclosure base wall (8075), or to attach theinner protective layer bottom edges (8240, 8245) with the input fuelmanifold (8015), and/or to attach the inner protective layer bottomedges (8240, 8245) to the intermediate enclosure (9000). Additionalholes or features as may be required to provide other mechanicalinterface features such as for attaching the inner protective layer(8220) to the hot zone enclosure end walls (8080, 8085), or forattaching the inner protective layer (8220) or the outer protectivelayer (8250) to the thermally conductive core (8200), or for providingfuel or cathode air flow ports, e.g. the combustion exhaust port (9060)or providing access for the fuel delivery conduit (8040) or forproviding a fuel conduit to the combustion region for use during coldstart-up, or for providing access for electrical interfaces for currentcollection, sensor attachment points, or the like, are also added beforeassembling the U-shaped primary enclosure wall assembly (8045).

After preparing the three flat sheets for assembly, includingelectroplating, machining, punching etc., the flat sheets correspondingwith the inner protective layer (8220) and the outer protective layer(8250) are each jointed to the flat sheet corresponding with thethermally conductive core (8200), e.g. by aligning and clamping thethree sheets in mating contact with each other and brazing the threesheets together to form a composite sheet metal structure which is stilla flat sheet. As noted above, the rolling direction of each sheet isidentified before cutting and assembling the sheets together andconsideration is given to orienting the grain direction with respect toa bending axis corresponding with the bend radius of the inner topportion (8225), the core top wall (8215) and the outer top portion(8265). The composite sheet metal structure is then bent to form theU-shaped structure shown in FIG. 9C with the inner protective layerpositioned to face the SOFC stack. The cylindrical radius has alongitudinal axis along the stack length axis (x). The bend radius isformed by a hydraulic bending device operable to bend or form thecomposite sheet metal structure at room temperature (air bending) on apress break, or the like. A bend radius that can be bent withoutdamaging the materials and managing undesirable consequences, such asspring back, separation of the individual sheets, or cracking along thebend axis is influenced by the material properties, e.g. hardness,tensile strength, the material thicknesses, the material graindirection, or the like and these properties are taken into considerationwhen determining the fabrication process of different embodiments of theU-shaped primary enclosure wall assembly (8045). Generally, it ispreferable to bend the material transverse to the material graindirection to avoid material cracking and separation of the joinedmaterial layers; however, this varies with material thickness. Thecomposite sheet metal structure can be preheated prior to bending, e.g.to 90 to 150° to reduce local stress during bending, thereby helping toprevent material separation and/or undesirable deformation. Otherforming methods, such as forging at higher temperatures, are usablewithout deviating from the subject technology.

4.12.5.3 Additional Fabrication Process Embodiments

As described in the first and second fabrication processes above, anyone of the inner protective layer (8220), the thermally conductive core(8200) and the outer protective layer (8250) can be formed from aunitary flat sheet stock that includes all three portions, including thetop portion that will be bent to a cylindrical radius and the two sideportions that extend from opposing edges of the cylindrical radius.According to a further fabrication process, two or three of the three ofthe unitary flat sheet stock portions can be joined together bycladding. The cladding may be carried out by a single cladding stepwherein the flat sheet stock corresponding with the inner protectivelayer (8220) and the outer protective layer (8250) are each jointed tothe flat sheet corresponding with the thermally conductive core (8200)in a single cladding or rolling step. Alternately, the cladding may becarried out in a two-step process wherein the flat sheet stockcorresponding with the inner protective layer (8220) or the outerprotective layer (8250) is joined to the flat sheet corresponding withthe thermally conductive core (8200), followed by joining the remainingflat sheet stock corresponding with the inner protective layer (8220) orthe outer protective layer (8250) to the flat sheet corresponding withthe thermally conductive core (8200) in a second cladding step.

In a cladding process a width of the cladded stock is transverse to therolling direction such that the width of the cladding stock ispreferably selected to correspond with a desired length dimension of theU-shaped primary enclosure wall assembly (8045), along the SOFC stackaxis (x).

From the cladding stock, a composite cladded sheet is cut topredetermined finished dimensions corresponding with forming the innerprotective layer, the thermally conductive core, and the outerprotective layer. Any additional processing of the composite claddedsheet is completed while the composite cladded sheet is still flat. Theadditional processing at least includes drilling, punching, or otherwiseforming the cathode chamber input ports (8095), plus adding other holesor formed features as may be required to provide mechanical interfaceelements used to attach the composite cladded sheet to the hot zoneenclosure base wall (8075), and/or to the input fuel manifold (8015)and/or to the intermediate enclosure (9000) and other holes or featuresas may be required to provide other mechanical interface features suchas for attaching the composite cladded sheet with the hot zone enclosureend walls (8080, 8085) or for providing fuel or cathode air flow ports,e.g. the combustion exhaust port (9060) or providing access for the fueldelivery conduit (8040) or for providing a fuel conduit to thecombustion region for use during cold start-up, or for providing accessfor electrical interfaces for current collection, sensor attachmentpoints, or the like, are also added before bending the single claddedflat sheet embodiment.

After preparing the composite cladded sheet, including electroplating,machining, punching, etc., the composite cladded sheet is bent to formthe U-shaped structure shown in FIG. 9C with the inner protective layerpositioned to face the SOFC stack. The cylindrical radius has alongitudinal axis along the stack length axis (x). The bend radius isformed by a hydraulic bending device operable to bend or form thecomposite sheet metal structure at room temperature (air bending) on apress break, or the like. A bend radius that can be bent withoutdamaging the materials and managing undesirable consequences, such asspring back, separation of the individual sheets, or cracking along thebend axis is influenced by the material properties, e.g. hardness,tensile strength, the material thicknesses, the material graindirection, or the like and these properties are taken into considerationwhen determining the fabrication process of different embodiments of theU-shaped primary enclosure wall assembly (8045). Generally, it ispreferable to bend the composite cladded sheet transverse to thematerial grain direction to avoid material cracking and separation ofthe joined material layers; however, this varies with materialthickness. The composite cladded sheet can be preheated prior tobending, e.g. to 90 to 150° or up to 1000° C. to reduce local stressduring bending, thereby helping to prevent material separation and/orundesirable deformation.

As further described in the first and second fabrication processesabove, any one of the inner protective layer (8220), the thermallyconductive core (8200) and the outer protective layer (8250) can beformed as three separate flat sheet stock elements corresponding withthe top portion that will be bent to a cylindrical radius and the twoside portions that extend from opposing edges of the cylindrical radius.In the case of the thermally conductive core (8200), it is fabricated bycutting each of the core top portion (8215) and the two core sidewallportions (8205, 8210) from a flat sheet of the core material. Thereafterany drilling, punching, machining, or electroplating is performed whilethe three core portions are still flat. The core top portion (8215) isthen bent to the desired cylindrical radius and then the two coresidewall portions (8205, 8210) are attached along different edges of thecylindrical radius to form the assembled thermally conductive core(8200).

Each of the inner protective layer (8220) and the outer protective layer(8250) are fabricated in the same manner wherein the inner and outer topportions (8225, 8265) and the inner and outer sidewall portions (8230,8235) and (8255, 8260) are formed from a flat sheet of the corematerial. Thereafter any drilling, punching, machining, orelectroplating is performed while the inner and outer protective layerportions are still flat. The inner and outer top portions (8225) and(8265) are then bent to the desired cylindrical radius, e.g. to matchthe corresponding inner and outer radius of the core top portion (8215).Thereafter the inner and outer top portions (8225, 8265) and the innerand outer sidewall portions (8230, 8235) and (8255, 8260) are mounted tothe assembled thermally conductive core, clamped in place, and thensoldered, welded, or otherwise mechanically attached to the thermallyconductive core.

As further described in the first and second fabrication processesabove, any one of the inner protective layer (8220), the thermallyconductive core (8200) and the outer protective layer (8250) can beformed as separate flat sheet stock elements corresponding with allthree of the top portion and the two side wall portions of the finalelement. Thereafter any drilling, punching, machining, or electroplatingis performed while the three separate flat sheet stock elements arestill flat. Thereafter each of the three separate flat sheet stockelements is bent to the desired cylindrical radius in three independentbending steps. Thereafter each of the three previously bent elements isassembled together, clamped and joined together by soldering, welding,or other mechanical fastening elements.

4.12.6 Thermal Conduction Through the Core Material

Referring to FIGS. 7B and 9C, thermal energy radiated from thecombustion region (8030) largely impinges on the combustion region wallportion (8060) and specifically on the inner top wall portion (8225).Additionally, gases moving through the combustion region (8030) largelytransfer thermal energy to the inner top wall portion (8225) byconvection. While the same thermal energy transfer mechanisms occur ateach of the inner protective layer sidewalls (8230, 8235), the rate ofthermal energy transfer from the gases in the combustion region wallportion (8060) is greater than the rate or thermal energy transfer fromgases that are not in the combustion region is less because thetemperature or the gases in the combustion region (8030) is higher.Thus, the rate of thermal energy transfer to the inner top wall portion(8225) is higher than the rate of thermal energy transfer to inner sidewalls (8230, 8235).

Thermal energy is transferred from the inner protective layer (8220) tothe thermally conductive core (8200) by a combination of thermalconductivity between mating surfaces of the inner protective layer(8220) and the thermally conductive core (8200) and radiation emittedfrom higher temperature surfaces to lower temperature surfaces.Additionally, thermal energy is transferred from higher temperatureregions of the inner protective layer, in this case the inner protectivetop portion (8225), to the lower temperature inner sidewalls (8230,8235) by thermal conduction through the material of the inner layer.Likewise, thermal energy is transferred from higher temperature regionsof the thermally conductive core, in this case the core top portion(8215), to the lower temperature core sidewalls (8205, 8210)) by thermalconduction through the material of the thermally conductive core.However, because the material of the thermally conductive core has amuch higher coefficient of thermal conductivity than the material ofinner the protective layer (8220), the rate of thermal energy transferby thermal conduction from the core top portion (8215) to each of thecore side walls (8205) and (8210) is seven times greater than the rateof thermal energy transfer from the inner the protective layer topportion (8025) to the inner protective layer side portions (8235) and(8240). The thermally conductive energy flow pathway from core topportion (8215) to each of the core side walls (8205) and (8210) is shownin FIG. 7B by dashed black lines with back arrows directed from the coretop portion (8215) to each of the core side walls (8205) and (8210). Thetransfer of thermal energy from the core top portion (8215) reduces athermal gradient present in the core material resulting in decrease inthe temperature of the core top portion and a corresponding increase thetemperature of the core side wall portions. Ideally the increasedthermal energy transfer rate in the thermally conductive core passivelyreduces the thermal gradient between the core top portion (8215) and thetwo core side walls (8205) and (8210) resulting in a reduction ofthermal gradient in each of the inner protective layer (8220) and theouter protective layer (8250). When the thermal gradient is reduced, theentire U-shaped primary enclosure wall assembly (8045) emits thermalenergy more uniformly along the gas flow axis (z) and thereforeredistributes thermal energy received from the combustion region (8030)to cathode air passing through the middle and lower volumes of thecathode chamber (8055) and the cathode input manifold (9070) and to theSOFC tubes (8010) and walls of the intermediate enclosure. Applicantsnote that a single core side wall such as either one of core side wall(8205) or (8210) is usable to provide the desired passive reduction inthe thermal gradient between the core top portion (8215) and only coreside wall without deviating from the present technology.

A significant benefit of the thermal gradient reduction along the gasflow axis (z) is a thermal gradient reduction along the SOFC stack(8005) along the gas flow (z) axis. By expanding the surface area of theanode and cathode layers that are maintained at an optimal SOFC reactiontemperature, an SOFC reaction yield is increased, e.g. as measured in DCcurrent generation per unit of syngas delivery. When only a portion ofthe anode and cathode surface area is participating in the SOFC reactionbecause non-participating portions of the anode and cathode surface areaare not at optimized reaction temperature, or when the cathode gas flowis not at optimized reaction temperature, reducing the thermal gradient,as described above, tends to convert non-participating SOFC reactionportions of the SOFC system to participating portions thereby increasingelectrical current output.

A second benefit is that a more uniform temperature of the SOFC stackalong the gas flow axis (z) potentially decreases damage to the SOFCfuel cells and other components caused by thermal expansion mismatch.The fuel cells are formed by three ceramic layers that each have adifferent coefficient of thermal expansion. Cracking or separation ofthe three ceramic layers is a common failure mode when the length changeof each material layer along the gas flow axis (z) during thermalcycling, e.g. start up or shut down, is different. Any reduction in atemperature gradient along the gas flow axis (z) potentially decreasesdamage to the SOFC fuel cells. Similarly, the hot zone enclosureassembly (8042) includes three walls, the thermally conductive core(8200) and the two protective layers (8220, 8250) formed from twodifferent materials each having a different coefficient of thermalexpansion. Separation and deformation of the three metal layers is apotential failure mode during thermal cycling when the different wallmaterial expand at different rates. The reduction in temperaturegradient variation along the gas flow axis (z) potentially decreasesdamage to the U-shaped hot zone enclosure assembly walls during thermalcycling.

Thermal conduction is described as a rate of thermal energy transfer(per unit time), also called heat flow or flux, which can be expressedin Watts or joules per second. Equation 1 below defines flux Q as,

Q=k A/d(ΔT)  EQUATION 1

wherein (Q) is the rate of thermal energy transfer in Watts, (k) is thecoefficient of thermal conductivity in W/(m° K), (A) is the area of thethermally conductive pathway e.g. in meters squared (m²), (d) is thelength of the conduction pathway, in meters, and (ΔT) is the temperaturegradient expressed in degrees Kelvin. In the case of the thermallyconductive core of the present embodiment, the length of the thermallyconductive pathway (d) is equal to the linear distance from the centerof the thermally conductive core top portion (8215) to a bottom edge ofone of the side portions (8205) and (8210). The dimensions of the area(A) are the product of the thickness of thermally conductive pathway andthe length of the thermally conductive pathway e.g. along the stacklength axis (x).

In a sample calculation, based on a thermal gradient ΔT of 200° K, acoefficient of thermal conductivity of 350 W/(m° K), a core thickness of2.5 mm (0.0025 m) and a length dimension (d) of 0.4 m, a unit area ofthe core material e.g. having square dimensions equal to the corethickness provides a heat flow or flux of 1.1 W per unit area whereinthe unit area is a square with side dimensions of 2.5 mm (0.1 inches).When the area dimension is over the entire stack length dimension (e.g.0.61 m or 24 inches), the heat flow or flux from thermal conductivity is267 W through each side wall. By comparison when the core material has acoefficient of thermal conductivity of 50 W/(m° K) the heat flow or fluxis 38.0 W through each side wall. Thus the thermally conductive core ofthe present embodiment potentially provides a 7× increase in heat flowthrough the thermally conductive core (8200) as compared to hot zoneenclosure walls fabricated from a conventional high temperatureenvironment material that has a coefficient of thermal conductivity of50 W/(m° K) or less, e.g. steel alloys, including Hastelloy, as well asMonel and Inconel.

4.12.7 Black Body Characteristics

In addition to thermal conduction, the thermally conductive core (8200)has black body characteristics wherein energy radiated per unit surfacearea per unit time across all wavelengths is proportional to the blackbody temperature to the fourth power. Black body radiation is depictedin FIG. 7B and described above including black body energy radiated fromgas flows. In the case of the thermally conductive core, radiationemitted thereby tends to be incident on the inner protective layer(8220) and on the outer protective layer (8250) and radiation absorbedby the thermally conductive core tends to be emitted by the innerprotective layer (8220) and on the outer protective layer (8250).

Black body radiant emittance is described in equation 2 with theassumption that the emitter has a surface emissivity of one which itlikely does not.

Q=σA(Tir ⁴ −Ts ⁴)  EQUATION 2

wherein Q is the rate of thermal energy transfer per unit time, inWatts, A is the area of the radiating surface in m², a is the Stefan'sconstant, (5.6703×10⁻⁸ W/s²K⁴), T_(ir) is the temperature of theirradiating surface and Ts is the temperature of the surrounding wallsin degrees Kelvin. As will be recognized, when thermal energy isthermally conducted, by the thermally conductive core (8200), from thecore top portion (8215) to lower ends of the core side walls (8230,8235), the temperature of the core top portion is decreased while thetemperature of the core side wall portions is increased. The change inboth wall temperatures alters the black body radiant emittance at eachlocation in proportion to the fourth power of the temperaturedifference. In an exemplary comparison, assume that the temperature ofthe lower ends of the primary enclosure side walls (8065, 8070) isincreased from 650° C. (923° K) to 700° C. (973° K), as a result ofthermal conduction through the core and assume that the temperature ofthe surrounding wall surfaces is unchanged, e.g. 550° C. (823° K) andthat the area of the radiation surface is one square centimeter(1.0×10⁻⁴ m²) as was used above. In this example, at a temperature of650° C. the rate of thermal energy transfer (radiant emittance), is1.514 W. At the increased temperature of 700° C., the rate of thermalenergy transfer is 2.481 W, which is a 64% increase in radiant emittanceper square centimeter

4.12.8 Temperature Measurements Demonstrate Passive Thermal GradientReduction

Referring now to FIGS. 10A, 10B, 11A and 11B, the passive reduction ofthermal gradient along the gas flow axis (z) of a plurality ofindividual fuel cells mounted on a test fixture is demonstrated bytemperature measurements made by five thermocouple devices. FIG. 10Aschematically depicts five SOFC fuel cells (10005) arranged on a testfixture (10000). The SOFC fuel cells are tube shaped with a cylindricalouter wall surrounding a fluid conduit. An anode surface is formed ontoan inside diameter of fluid conduit of each fuel cell and a cathodesurface is formed onto an outside diameter of each fuel cell. The testfixture includes a fuel input manifold (10010) disposed to support eachfuel cell from a bottom end thereof. A syngas flow is delivered intoeach tube fluid conduit by the fuel input manifold. A cathode chamber isformed by enclosing the test fixture fuel cells within a test enclosuredesigned to provide the same functionality as the hot zone enclosureassembly (8042) described above. As described below, two test enclosureunits were constructed. A first test enclosure does not include thethermally conductive core of the present technology and a second testenclosure that includes the thermally conductive core of the presenttechnology.

The test fixture includes five thermocouples (TC1 through TC5) locatedat five locations indicated by five star symbols (10030), shown in FIG.10A. The five thermocouples (TC1-TC5) are distributed along the gas flowaxis (z) and are evenly spaced apart. The thermocouples are mountedbetween the fuel cells (10005) or proximate to a surface of one of thefuel cells. The length of each fuel cell (10005) along the gas flow axis(z) is selected to match desired fuel cell dimensions, e.g. 150-300 mm(6-12 inches). Thermocouple TC5 is positioned approximately 15 mm, (0.6inches) from SOFC stack upper end and the remaining thermocouples evenlydistributed along the cell length. Each thermocouple (TC1 through TC5)was electrically interfaced with an electronic controller, not shown.The electronic controller is configured to receive temperature signalsfrom each of the five thermocouples, to process the temperature signals,e.g. to compare the temperature signals to a temperature calibrationtable, to store a series of temperature signals detected by eachthermocouple over a time duration and to determine average temperaturevalues over given time periods.

During a first set of temperature measurements, each of the fivethermocouples was operated to monitor temperature at each of the fivestar locations (10030) over a two and one half hour start-up throughcool-down operating cycle to record temperature data at predeterminedtime intervals and to calculate an average temperature. The first set oftemperature measurements was recorded as the test fixture was heatedfrom a cold start to an operating temperature corresponding withgenerating electrical current output, recorded during the entire timethe test fixture was generating electrical current and recorded as thetest fixture was cooling down to the cold start temperature. In thepresent example, the operating temperature corresponding with generatingelectrical current output was maintained for about one and a half hoursand the start-up and cool down phase each lasted about 30 minutes.

During the first set of temperature measurements the test fixture wasoperated inside a furnace without installing a thermally conductive coreto enclose the stack.

The first set of temperature measurements is shown graphically in FIG.10B by the black bars (10035) wherein each black bar indicates theaverage temperature corresponding with one thermocouple during steadystate operation. The dashed lines (10050) extend between each black bar(10035) and one of the thermocouples (TC1-TC5) to indicate whichthermocouple the average temperature value relates to. Each temperaturemeasurement corresponding with a black bar (10035) is an averagetemperature measured by the corresponding thermocouple during electricalcurrent output by the test fixture. As shown by the black bars (10035)the average temperature measured at TC1 is approximately 775° C., theaverage temperature measured at TC2 is approximately 700° C., theaverage temperature measured at TC3 is approximately 720° C., theaverage temperature measured at TC4 is approximately 630° C. and theaverage temperature measured at TC5 is approximately 640° C. Thetemperatures were averaged over about a one hour operating cycle.

During the second set of temperature measurements the test fixture wasoperated with the second test enclosure assembly that did include athermally conductive core. The second test enclosure assembly used theU-shaped primary enclosure wall assembly (8045) described above thatincluded the inner protective layer (8220), the thermally conductivecore (8200) and the outer protective layer (8250) as shown in FIG. 9C.The inner protective layer (8220) and outer protective layer (8250) ofthe second test enclosure assembly were formed from the Monel which hasa coefficient of thermal conductivity of about 22.8 (W/m° K) and thethickness of the inner and outer protective layers was about 4.0 mm(0.16 inches). The thermally conductive core (8200) of the second testenclosure was formed from a copper alloy that had a coefficient ofthermal conductivity of about 350 (W/m° K) and the thickness of thethermally conductive core corresponding with the second test enclosurewas about 3.0 mm (0.12 inches).

The second set of temperature measurements corresponding with the secondtest enclosure is shown graphically in FIG. 10B by the white-stripedbars (10040) wherein each white-striped bar is associated with onethermocouple as indicated by the dashed lines (10050) that extendbetween each white-striped bar (10040) and one of the thermocouples(TC1-TC5). Each temperature measurement corresponding with awhite-striped bar is an average temperature recorded during the periodwhen the test fixture was generating electrical current output. As showby the white-striped bars (10040) the average temperature measured atTC1 is approximately 710° C., the average temperature measured at TC2 isapproximately 720° C., the average temperature measured at TC3 isapproximately 730° C., the average temperature measured at TC4 isapproximately 740° C. and the average temperature measured at TC5 isapproximately 710° C.

As predicted in the description above, the thermal gradient along thestack gas flow axis (z) is reduced by addition of the copper core in thesecond test fixture. The temperature measurement data for the first setof temperature values measured using the first test enclosure assemblythat does not include a thermally conductive core and the second set oftemperature values measured using the second test enclosure assembly(that includes the thermally conductive core) are listed in Table 1below. As is readily apparent from the data listed in Table 1 and showngraphically in FIG. 10B, addition of the thermally conductive core tothe second test enclosure assembly reduces the thermal gradient alongthe gas flow axis (z) of the test fixture fuel cells (10005). Applicantsfurther note that in the second data set corresponding with the secondtest enclosure assembly that includes the thermally conductive core, thehighest temperature measured was at TC4 indicating that addition of thethermally conductive core actually shifts the position of peaktemperature away from the combustion region (8030) to a point that isbelow the mid-point of the fuel cells.

TABLE 1 Temperature change (° C.) at each temperature measurementlocation Thermocouple ID TC1 TC2 TC3 TC4 TC5 Temperature range Test 1 nocore 775 700 720 630 640 145° C. between TC1 and TC4 Test 2 core 710 720730 740 710 30° C. between TC4 and included TC1 and between TC4 and TC5Temperature −65 +20 +10 +110 +70 change Test 1 to test 2

FIG. 11A graphically depicts temperature measurement data recordedduring the first test cycle utilizing the first test enclosure assemblythat does not include a thermally conductive core. A vertical axis ofthe graphical representation represent of FIG. 11A corresponds withtemperature in ° C. as measured by the five thermocouples and ahorizontal axis of FIG. 11A corresponds with time in hours. Thegraphical representation of FIG. 11A includes five different temperaturevs time plots with one plot corresponding with for each of the fivethermocouple locations. A legend (10045) shows which data plotscorrespond with which thermocouple location (TC1, TC2, TC3, TC4, TC5).

Similarly, FIG. 11B graphically depicts temperature measurement datarecorded during the second test cycle utilizing the second testenclosure assembly that does include a thermally conductive core. Avertical axis of the graphical representation represent of FIG. 11Bcorresponds with temperature in ° C. as measured by the fivethermocouples and a horizontal axis of FIG. 11B corresponds with time inhours. The graphical representation of FIG. 11B includes five differenttemperature vs time plots with one plot corresponding with for each ofthe five thermocouple locations. A legend (10055) shows which data plotscorrespond with which thermocouple location (TC1, TC2, TC3, TC4, TC5).

A comparison of the two plots reveals that during the startup cycle,when the temperature of the thermocouples increases from 100° C. toabove 700° C. over a period of about 30 minutes, the rate of temperatureincrease at each of the five thermocouple positions was nearly the samewhen the thermally conductive core was in place (FIG. 11B) and clearlynot the same without the thermally conductive core in place, (FIG. 11A).This is apparent when comparing the startup period of FIG. 11A with thestart-up period of FIG. 11B. FIG. 11A indicates that the rate oftemperature increase in ° C./unit time was greatest at the thermocoupleposition (TC1) and least at the thermocouple position (TC5). Conversely,FIG. 11B indicates that the rate of temperature increase in ° C./unittime was much more uniform at over the five thermocouple positions (TC1,TC2, TC3, TC4, TC5) throughout the start up period.

When different portions of individual fuel cells (8010) are heated atdifferent rates, this can lead to layer cracks and or chipping of thefuel cell ceramic layers as well as failures of the interfaces betweenceramic and metallic components in the stack. Similarly, when differentportions of the hot zone enclosure assembly walls are heated atdifferent rates, this can lead to layer delamination and or buckling ofthe thermally conductive core and the inner and outer protective layers.

4.12.9 Additional SOFC System Embodiments

Referring now to FIG. 12, a non-limiting exemplary SOFC system (12000)includes two hot zone enclosure assemblies (12042). The two hot zoneenclosure assemblies are each disposed inside an intermediate enclosure(9000), shown in FIGS. 9, 16B and 17, and spaced apart along the stacktransvers with axis (y). Each hot zone enclosure assembly (12042)includes an SOFC stack (8005), a fuel input manifold (8015) that isfluidly connected to a fuel reformer (8035) by a fuel delivery conduit(8040) and a L-shaped primary enclosure wall assembly (12045). Each SOFCstack (8005) is enclosed within a different cathode chamber (12055).Each cathode chamber (12055) is bounded in part by one of the L-shapedprimary wall assemblies (12045) and in part by intermediate enclosurebase wall (9010) side walls (9015 or 9020), shown in FIG. 13.Additionally, each cathode chamber can be bounded by opposing primaryenclosure end walls (8080, 8085) and a primary enclosure base wall(8075) shown in FIG. 9C.

FIG. 13 depicts two L-shaped primary enclosure wall assemblies (12045),with one disposed over a first SOFC stack (8005) and the other disposedover another SOFC stack (8005). As shown in FIG. 13A each L-shapedprimary enclosure wall assembly (12045) is formed with three wallportions, combustion region curved wall portion (12062), combustionregion a flat wall portion (12064) extending from a first edge of thecurved wall portion and a primary enclosure sidewall (12070) extendingfrom a second edge of the curved wall portion. The combined curved wallportion (12060) and combustion region flat wall portion (12064) provideand upper boundary of a cathode chamber (12055), described below, andform an upper boundary of the combustion region (8030) in order toreceive thermal energy therefrom. The sidewall portion extends from anedge of the curved wall portion and is disposed along the gas flow axis(z) between SOFC tube output ends (8025) and SOFC tube input ends(8020).

Each L-shaped primary enclosure wall assembly (12045) defines a cathodechamber (12055). The cathode chamber (12055) encloses a correspondingSOFC stack (8005) and a combustion region (8030) such that the cathodelayer formed on outside surfaces of each individual fuel cell (8010) isexposed to the cathode chamber (12055). Cathode chambers (12055) arebounded in part by a corresponding L-shaped primary enclosure wallassembly (12045), by an intermediate enclosure side wall (9015 or 9020)and by the intermediate enclosure bottom wall (9010) or by the fuelinput manifold (8015), or another bottom wall e.g. (8075) shown in FIG.9C. Each L-shaped primary enclosure wall assembly (12045) defines adifferent cathode chamber (12055).

The SOFC system (12000) includes a recuperator chamber (9050) and a hotzone exhaust conduit (9055) each formed inside the intermediateenclosure (9000). The recuperator chamber (9050) and hot zone hot zoneexhaust conduit (9055) together form a counter flow gas to gas heatexchanger described above in the description of FIGS. 7A and 7B. Ambienttemperature cathode air flow is received into the recuperator chamber(9050) through the cathode input port (9040) and exhaust gases areexpelled from the exhaust conduit through a hot zone exhaust port(9045).

Inside the recuperator chamber (9050) incoming cathode air flow, e.g.ambient temperature air, is heated by convection and by radiation beingemitted from walls of the recuperator chamber and especially a sharedwall (9075) which separates the hot zone exhaust conduit (9055) from therecuperator chamber (9050). The heated cathode air flow is forcedthrough the recuperator chamber (9050) and exits from the recuperatorchamber through one or more recuperator exit ports (9065) to a cathodeinput manifold (13070). The cathode air flow source includes a variablespeed air moving device (e.g., a fan) that can be controlled to increaseor decrease the flow rate of the incoming cathode air flow in accordancewith electrical output demands and other process control commands.

The hot zone exhaust conduit (9055) receives a hot gas mixture from twocombustion zones (8030) through two combustion exhaust ports (9060)wherein each combustion exhaust port (9060) extends from one of the twocombustion regions (8030) to the hot zone exhaust conduit (9055). Insidethe hot zone exhaust conduit (9055) the hot gas mixture is cooled asenergy is convectively and radiatively transferred to the walls of thehot zone exhaust conduit (9055). The hot gas mixture passes from thecombustion region (8030) through the exit the SOFC hot zone through thehot zone hot zone exhaust port (9045) and finally exits the SOFC hotzone through the hot zone hot zone exhaust port (9045).

Each of the recuperator chamber (9050) and the hot zone exhaust conduit(9055) is preferably disposed along the full length of the SOFC stackalong the stack length axis (x). Each of the cathode input port (9040),the hot zone exhaust port (9045), and the two combustion exhaust port(9060) can be implemented as a single instance of all three ports e.g.posited at the center or at one end of the stack length along the lengthaxis (x) or a plurality of cathode input ports (9040), hot zone exhaustports (9045) and combustion exhaust ports (9060) can be spaced apartalong the stack length axis (x) to more uniformly distribute cathode airflow to individual fuel cells and to more uniformly distribute exhaustgases from the SOFC hot zone. The port apertures may be circular,slotted, or other port shaped instances that are disposed along thestack length axis (x). Alternately, each of the recuperator chamber(9050) and the hot zone exhaust conduit (9055) can be implemented as asingle chamber instance extending along the entire stack length axis (x)or the recuperator chamber and exhaust conduit can be configured as aplurality of separate chamber and conduit instances disposed side byside along the stack length axis (x), with each separate chamberinstance provided with its own cathode input port (9040), and/or the hotzone exhaust port (9045) and with one combustion exhaust port (9060) foreach cathode chamber.

As shown in FIG. 12, a single cathode input manifold (13070) is sharedby the two cathode chambers (12055). A cathode input manifold (13070)top boundary is defined by a exhaust conduit bottom wall (9059).Opposing cathode input manifold side boundaries are defined by outsidesurfaces of each of the two L-shaped primary enclosure wall assemblies(12045) and the cathode input manifold (13070) has a bottom boundarydefined by the intermediate enclosure bottom wall (9010) or anotherbottom wall (8070) described above, or both. Each end of the cathodeinput manifold (13070) can be bounded by intermediate enclosure endwalls (9025, 9030) or by end walls (8065, 8085) described above.

Cathode gas flow is shown in FIG. 12 by solid flow lines with arrows.The cathode air flow enters through the cathode input port (9040),passes through the recuperator chamber (9050) and then enters thecathode input manifold (13070) through each of two recuperator exitports (9065). Inside the cathode input manifold (13070) the cathode airflow is guided downward from the recuperator exit ports (9065) to entertwo sets of cathode chamber input ports (8095), with one set of cathodeflow passages corresponding with each L-shaped primary enclosure wall(12045). The cathode air then passes from the cathode input manifold(13070) to each of the two cathode chambers (12055). Inside the cathodechambers, the cathode gas flows upward past the exposed cathode surfacesof the SOFC stack until reaching the combustion region (8030) wherespent cathode air flow is mixed with spent fuel. The further flow pathof the mixture of spent fuel and spent cathode air is indicated bydashed flow lines with arrows which show the mixture flowing from thecombustion region (8030) through the two combustion exhaust ports(9060), one for each cathode chamber, and through the hot zone exhaustconduit (9055) where the mixture transfers thermal energy to the sharedwall (9075) and other wall surfaces before exiting the SOFC systemthrough the hot zone hot zone exhaust port (9045). The combustion regionwall portions (12060) formed with a combustion region curved wallportion (12062) and the flat combustion region wall (12264) eachextending from a different intermediate enclosure side was (9015) or(9020) side wall to form a top boundary of the corresponding cathodechamber (12055) and the primary enclosure sidewall (12070) extendingfrom a second edge of the combustion region curved wall portion (12062)forms a side boundary of the corresponding cathode chamber (12055). TheL-shaped primary enclosure wall (12045) is disposed along the fulllength of the stack length axis (x) and may extend further beyond thefull stack length dimension.

Referring to FIGS. 13B, and 14, each L-shaped primary enclosure wallassembly (12045) includes a thermally conductive core (12200), protectedby an inner protective layer (12220) and an outer protective layer(12250). Thermally conductive core (12200) is substantially similar inmaterial, construction, function, and thermal characteristics as thethermally conductive core (8200) discussed herein in relation to FIGS.7A, 7B, 8B, 9A, 9B, and 9C comprising a core material having acoefficient of thermal conductivity of more than 100 W/(m° K) andpreferably more than 200 W/(m° K) such as one or more of copper,molybdenum, aluminum nickel, beryllium, iridium, rhodium, silver,tungsten, or alloys or combinations therefore that can be fabricatedwith a desired thermal conductivity and that can reliably meet thestructural requirements at the hot zone operating temperatures. In aparticular exemplary, non-limiting embodiment, thermally conductive core(12200) comprises a copper mass having a thermal conductivityapproximately ranging from 370 W/(m° K) at 500° C. and 332 W/(m° K) at1027° C.

The L-shaped primary enclosure wall assembly (12045) includes an innerprotective layer (12220) and outer protective layer (12250) configuredto protect the thermally conductive core wall (12200) from oxidation.Application of the inner protective layer and the outer protective layer(12220, 12250) is described above. In a first embodiment each of theinner protective layer (12220) and the outer protective layer (12250)comprises nickel plating applied to the thermally conductive core(12200) by an electro-plating process to a thickness of at least 0.0005inches and ranging up to 0.002 inches or more. The nickel plating isapplied in order to prevent oxygen diffusion there through at operatingtemperatures of 350 to 1200° C. In a second embodiment, the innerprotective layer (12220) comprises an inner sheet metal layer formed tomate with inside surfaces of the thermally conductive core (12200) andthe outer protective layer (12250) comprises and outer sheet metal layerformed to mate with outside surfaces of the thermally conductive core(12200) in order to prevent oxygen diffusion through either of theprotective layers at operating temperatures of 350 to 1200° C.

The inner and outer protective sheet metal layers are fabricated withthe same materials described above for inner protective layer (8220) andouter protective layer (8250) shown in FIG. 9C and described above. Inan exemplary, non-limiting embodiment, each inner protective layer(12220) and outer protective layer (12250) is formed from a materialthat is resistant to corrosion and especially oxidation at SOFCoperating conditions. In a preferred embodiment each inner protectivelayer (12220) and outer protective layer (12250) is fabricated fromferritic stainless steel such as Alloy18 SR® Stainless Steel, e.g.distributed by Rolled Metal Products, of Alsip, TL, US. As shown in FIG.12, the inner protective layers (12220) face the cathode chamber (12055)and outer protective layers (12250) face cathode input manifolds(13070).

In an exemplary operating mode, thermal energy generated in combustionregion (8030) is transferred by radiation and convection to combustionregion wall (12060). The thermal energy absorbed by the combustionregion wall is passively conducted through inner protective layer(12220) to the conductive core (12200). The thermal energy that reachesthe conductive core is passively conducted, via conductive core (12200),to lower temperature regions of the thermally conductive core e.g. to adistal end of the primary enclosure side wall (12070). As a result, atemperature gradient present in the core (12200) is reduced. Duringsteady state operation, a thermal gradient between the combustion regionwall (12060) and the bottom end of the primary enclosure side wall(12070) is reduced. Thermal energy is exchanged, primarily viaradiation, between each L-shaped primary enclosure wall assembly (12045)and SOFC cells (8010). However, when the thermal gradient between thecombustion region wall and the sidewalls is reduced, a correspondingthermal gradient along the length of each SOFC cell along the gas flowaxis z is also reduced. Thermal energy is conducted between theconductive core (12200) and the outer protective layer (12250). Thermalenergy exchange, via conduction and convection, between the outerprotective layer (12250) and cathode gas flowing within the cathodeinput manifolds (13070, 14070, 15070) heats the cathode gas.

Referring to FIG. 13B, in a non-limiting exemplary embodiment, L-shapedprimary enclosure wall assembly (12045) includes inner protective layer(12220) formed as a single piece of material having an inner side wallportion (12230), an inner curved wall portion (12225) and an inner topwall portion (12227). Exemplary conductive core (12200) is preferablyformed from a single piece of material having a core side wall portion(12210), a core curved wall portion (12215) and a core top wall portion(12217). As shown in FIG. 13B, outer protective layer (12250) is formedas three separate parts: an outer side wall portion (12260), a outercurved wall portion (12265), and outer top wall portion (12267). Theinner protective layer (12220), the thermally conductive core (12200),and outer protective layer (12250) can be formed and joined togetherusing any of the methods discussed in relation to the U-shaped primaryenclosure wall assembly (8045) as illustrated in, for example, FIG. 9C.

Referring to FIG. 14 an SOFC system (14000) comprises a single L-shapedhot zone enclosure assembly (14042) enclosing a single SOFC stack (8005)and input fuel manifold (8015) and fuel delivery conduit (8040). TheL-shaped hot zone enclosure assembly (14042) is described above in thedescription related to FIGS. 12-13B. The single L-shaped hot zoneenclosure assembly (14042) is installed inside an intermediate enclosure(9000) sized to receive a single L-shaped hot zone enclosure assembly(14042). The intermediate enclosure provides a recuperator chamber(9050), a hot zone exhaust port (9045), a cathode input port (9040), acathode input manifold (14070) and a cathode chamber (12055) alldescribed above. An advantage of the SOFC hot zone (14000) is itscompact size.

Referring to FIG. 15, an SOFC hot zone (15000) comprises a hot zoneenclosure assembly (15042) shown in a schematic view. The hot zoneenclosure assembly (15042) includes two SOFC stacks (8055), two fuelinput manifolds (8015) and a U-shaped primary enclosure wall assembly(8045) each enclosing one of the two SOFC stacks and forming an isolatedcathode chamber (8055) surrounding each SOFC stack as described hereinin relation to FIGS. 7A, 7B, 9A, 9B, and 9C. A cathode input manifold(15070) is sized to receive the hot zone enclosure assembly (15042)therein and is bounded by inward facing surfaces of intermediateenclosure side walls (9015, 9020) and intermediate enclosure bottom wall(9010), by outward facing surfaces of each of the two U-shaped primaryenclosure wall assemblies (8045), by the bottom wall (9059) of the hotzone exhaust conduit (9055), and by inward facing surfaces of hot zoneenclosure end walls (8080, 8085) show in FIG. 9C.

4.12.10 Intermediate Enclosure

The hot zone enclosure wall assemblies (12045, 14045, 15042) eachinstalls inside an intermediate enclosure (9000), shown in an isometricview in FIGS. 16b and 17. The intermediate enclosure is formed as achamber comprising opposing intermediate enclosure top wall (9005) andintermediate enclosure bottom wall (9010), opposing intermediateenclosure side wall (9015) and intermediate enclosure side wall (9020)and opposing intermediate enclosure end wall (9025) and intermediateenclosure end wall (9030). The intermediate enclosure (9000) enclosesfuel delivery conduits (8040) in a gap between intermediate enclosureend wall (9025) and hot zone enclosure end wall (8080). The intermediateenclosure includes a cathode input port (9040) for receiving a cathodeair flow there through, and a hot zone exhaust port (9045) for expellingexhaust out therefrom. The intermediate enclosure includes a startupfuel inlet port (8145) for receiving a flow of fuel during a startupoperating mode of the SOFC system and for directing the flow of fuel toeach of startup burner element (8155). Each of the ports (8145), (9040),and (9045) passes through a wall of the intermediate enclosure asrequired to direct gas flow to receiving area interface. In anon-limiting exemplary embodiment, the fuel ports passes through one ofthe side walls (9015, 9020) and each of the cathode gas input port(9040) and the hot zone exhaust port (9045) pass through theintermediate enclosure top wall (9005). The intermediate chamber (9000)also encloses or partially encloses the recuperator chamber (9050) and ahot zone hot zone exhaust conduit (9055), hot zone exhaust port (9045),cathode input port (9040), combustion exhaust ports (9060, 9060 a, 9060b), recuperator exit ports (9065) each of which function as described inrelation to FIGS. 7A, 7B, and 8A.

4.12.11 Outer Enclosure

As shown in FIGS. 16A, 16B, and 17 the intermediate enclosure (9000)installs inside an insulating layer (2012) which preferably includes topand bottom portions, not shown, to thermally insulate the intermediateenclosure surfaces. The intermediate enclosure and the surroundinginsulation layer each install inside an outer enclosure (16000). In afirst non-limiting exemplary embodiment, outer enclosure (16000)includes two opposing outer enclosure side walls (16015) and twoopposing outer enclosure end walls (16010), an outer enclosure top wall(16005) and an opposing outer enclosure bottom wall (16002). Preferablythe outer enclosure walls are thermally insulated from the intermediateenclosure (9000). In a preferred embodiment the thermal insulation layer(2012) is disposed between the inner enclosure (9000) and the outerenclosure (16000) and is configured to prevent a temperature of theouter walls from exceeding a maximum temperature, e.g. 60° C. greaterthan ambient temperature. The outer enclosure is formed to providevarious input and output ports to interface with anode gas fuel andcathode air conduits, exhaust gas exit ports, electrical power outputfrom the SOFC stack and an interface to a control system which includetemperature and electrical power sensors, fluid flow meters, and othercontrol elements as may be required. Preferably the outer enclosure isformed with a structural integrity designed to protect the innerintermediate enclosure, the fuel cells, and other internal systems fromdamage from shock or moisture and to prevent contaminants from escapingfrom the SOFC hot zone and/or from entering the SOFC hot zone fromoutside.

The outer enclosure (16000) is preferably formed by metal walls e.g.steel, stainless steel, aluminum or the like. In some embodiments, theouter enclosure or portions of the outer enclosure or elements extendingfrom inside the outer enclosure may be utilized as a radiator to radiatethermal energy that has been absorbed from inside the SOFC system, e.g.from the fuel reformer, exhaust gas passages, or recuperator to airsurrounding the SOFC hot zone. All patents, patent applications andother references disclosed herein are hereby expressly incorporated intheir entireties by reference.

It will also be recognized by those skilled in the art that, while thetechnology has been described above in terms of preferred embodiments,it is not limited thereto. Various features and aspects of the abovedescribed technology may be used individually or jointly. Further,although the technology has been described in the context of itsimplementation in a particular environment, and for particularapplications (e.g. Solid oxide fuel cell systems), those skilled in theart will recognize that its usefulness is not limited thereto and thatthe present technology can be beneficially utilized in any number ofenvironments and implementations where it is desirable to increasethermal energy transfer by thermal conduction using high thermalconductivity materials at high temperatures and in corrosiveenvironments. Accordingly, the claims set forth below should beconstrued in view of the full breadth and spirit of the technology asdisclosed herein.

1-13. (canceled)
 14. A Solid Oxide Fuel Cell (SOFC) system as recited inclaim 36, wherein: a portion of the thermal mass is a primary wallassembly (8045) configured to enclose a cathode chamber (8055) thereinand formed to provide one or more thermally conductive pathwaysextending between different regions of the primary wall assembly; theelongated SOFC stack (8005) is enclosed by the primary wall assembly; afirst portion of the primary wall assembly receives heat from acombustion region enclosed by the primary wall assembly and conducts theheat to a second portion of the primary wall assembly; and the secondportion radiates heat to a first portion of the solid oxide fuel celland transfers heat to a cathode air flow passing by surfaces of theprimary wall assembly by heat exchange. 15-21. (canceled)
 21. A SolidOxide Fuel Cell (SOFC) system as recited in claim 14, further comprisingat least one of the outer layer on the primary wall assembly that formsan oxide layer during operation of the SOFC stack.
 22. A hot zoneenclosure assembly (8042) for balancing temperature in a solid oxidefuel cell (SOFC) stack, the hot zone enclosure assembly comprising: acombustion region wall defining a combustion region around an outlet endof the SOFC stack for collecting anode fuel and cathode air exiting theSOFC stack, wherein the anode fuel and the cathode air, burn andgenerate heat in the combustion region so that the heat is absorbed bythe combustion region wall; and a sidewall depending from the combustionregion wall along the SOFC stack, wherein: the sidewall has a distal endadjacent an inlet end of the SOFC stack; the absorbed heat passes byconduction to the distal end of the sidewall; and the absorbed heatradiates from the distal end to the inlet end of the SOFC stack tobalance temperature along the SOFC stack.
 23. The hot zone enclosureassembly (8042) of claim 22 further comprising: a second sidewalldepending from the combustion region wall opposing the sidewall; a hotzone enclosure base wall (8075) coupled to the sidewall (8070) and thesecond sidewall; and first and second hot zone enclosure end walls(8080, 8085) coupled to the combustion region wall, the sidewall, andthe second sidewall to enclose the SOFC stack.
 24. The hot zoneenclosure assembly (8042) of claim 22, wherein the combustion regionwall comprises a thermally conductive core.
 25. The hot zone enclosureassembly (8042) of claim 24, wherein the thermally conductive core has acoefficient of thermal conductivity that is greater than 100 W/m° K attemperatures above 350° C.
 26. The hot zone enclosure assembly (8042) ofclaim 24, wherein the thermally conductive core is fabricated frommaterial selected from the group consisting of: copper; molybdenum;aluminum: aluminum copper; copper nickel alloys; and combinationsthereof.
 27. The hot zone enclosure assembly (8042) of claim 22 furthercomprising a fuel input manifold (8015) adjacent to an inlet end of theSOFC stack.
 28. The hot zone enclosure assembly (8042) of claim 22wherein the SOFC stack is configured to receive a cathode gas from anexternal air flow source, the cathode gas reacting with a cathode layersurface of a fuel cell within the SOFC stack.
 29. The hot zone enclosureassembly (8042) of claim 28 wherein the fuel cell stack shape isselected from the group consisting of: oval shaped, square shaped,rectangular, and triangular.
 30. The hot zone enclosure assembly ofclaim 22, wherein the SOFC stack is at least two rows of SOFC cellsseparated by the sidewall.
 31. The hot zone enclosure assembly of claim30, further comprising: a first outer sidewall depending from thecombustion region wall and enclosing a first of the at least two rowswith the sidewall; and a second outer sidewall depending from thecombustion region wall and enclosing a second of the at least two rowswith the sidewall, wherein the first and second outer sidewalls receiveheat from the combustion region wall by thermal conduction and radiateheat to the inlet end of the SOFC stack.
 32. A method of manufacturingan enclosure wall assembly, the method comprising: a) forming athermally conductive core; b) shaping the thermally conductive core,such that an exterior surface of the thermally conductive core ispositioned to face an SOFC stack; and c) shielding the thermallyconductive core from oxidation with a protective layer such that contactbetween the thermally conductive core is protected by the protectivelayer from exposure to oxygen rich cathode air flow.
 33. The method ofmanufacturing an enclosure wall assembly in claim 32, further comprisingforming a plurality of thermally conductive cores.
 34. The method ofmanufacturing an enclosure wall assembly in claim 32, wherein shapingthe thermally conductive core comprises shaping the thermally conductivecore into a T-shaped structure.
 35. The method of manufacturing anenclosure wall assembly in claim 32 further comprising forming inputports that pass through the protective layer.
 36. A Solid Oxide FuelCell (SOFC) system comprising: an elongated SOFC stack disposed inside ahot zone cavity along an axis, wherein the elongated SOFC stack has atop end and a bottom end; and a thermal mass receiving heat from the hotzone cavity, conducting heat from the top end to the bottom end alongthe axis, and radiating heat to the bottom end radially with respect tothe axis.